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Abstract:

A drive unit includes an ultrasonic actuator, which has an actuator body
formed using a piezoelectric element and outputs a driving force by
vibration of the actuator body, and a control section which induces
vibration in the actuator body by supplying a plurality of AC voltages to
the piezoelectric element. The control section provides, in combination,
phase control, which controls the driving force by adjusting a phase
difference between a first and a second AC voltages, and wave-number
control, which controls the driving force by adjusting the wave number
included in a predetermined burst period in each AC voltage.

Claims:

1. A drive unit, comprising:a vibratory actuator having an actuator body
formed using a piezoelectric element, and configured to output a driving
force by vibration of the actuator body; anda control section configured
to induce vibration in the actuator body by supplying a plurality of
pulse signals or a single-phase pulse signal to the piezoelectric
element, whereinthe control section provides, in combination, either
phase control, which controls the driving force by adjusting a phase
difference between the plurality of pulse signals, or duty-cycle control,
which controls the driving force by adjusting a duty cycle of the
single-phase pulse signal, and wave-number control, which controls the
driving force by adjusting the number of pulses included in a
predetermined burst period in each of the pulse signals or in the pulse
signal.

2. The drive unit of claim 1, whereinin the wave-number control, the
control section adjusts the number of pulses included in the burst period
based on a parameter associated with the phase difference in the phase
control or a parameter associated with the duty cycle in the duty-cycle
control.

3. The drive unit of claim 2, whereinthe control sectionincrements the
number of pulses included in the burst period by one when the parameter
has been greater than a predetermined first threshold during a time
period longer than a predetermined first duration, anddecrements the
number of pulses included in the burst period by one when the parameter
has been less than a second threshold, which is less than the first
threshold, during a time period longer than a predetermined second
duration.

4. The drive unit of claim 2, whereinthe control sectiontentatively
increments the number of pulses included in the burst period by one when
the parameter has been greater than a predetermined first threshold
during a time period longer than a predetermined first duration; restores
the number of pulses to the original value after a predetermined first
holding time has elapsed; and then, if the parameter has again been
greater than the first threshold during a time period longer than the
first duration, ultimately increments the number of pulses by one,
andtentatively decrements the number of pulses included in the burst
period by one when the parameter has been less than a second threshold,
which is less than the first threshold, during a time period longer than
a predetermined second duration; restores the number of pulses to the
original value after a predetermined second holding time has elapsed; and
then, if the parameter has again been less than the second threshold
during a time period longer than the second duration, ultimately
decrements the number of pulses by one.

5. The drive unit of claim 2, whereinthe control section divides the
parameter into a plurality of regions based on a value thereof, and
assigns a number of pulses included in the burst period to each of the
regions.

6. The drive unit of claim 5, whereinthe control section sets each lower
limit value of the regions to which corresponding numbers of pulses are
assigned for a case where the parameter decreases in value, below each
lower limit for a case where the parameter increases in value.

7. The drive unit of claim 2, whereinthe control section adjusts the
number of pulses included in the burst period depending on a value of the
parameter, and adjusts the pulse width of at least one of the pulses
included in the burst period.

8. The drive unit of claim 7, whereinthe control section adjusts the
number of pulses included in the burst period and the pulse width of the
at least one pulse so that the sum of the pulse widths of the pulses
included in the burst period is proportional to the value of the
parameter.

9. The drive unit of claim 2, whereinthe control section obtains an amount
of control for the phase difference or an amount of control for the duty
cycle using PID control based on a deviation between an actual
operational condition and a target operational condition of a driven
object driven by the vibratory actuator, andthe parameter in the
wave-number control is at least one of an integral term or a proportional
term of the PID control.

10. The drive unit of claim 2, whereinthe control section obtains an
amount of control for the phase difference or an amount of control for
the duty cycle using feedback control based on a deviation between an
actual operational condition and a target operational condition of a
driven object driven by the vibratory actuator; includes an observer
which is designed based on models of the driven object and the vibratory
actuator; and corrects the amount of control for the phase difference or
the amount of control for the duty cycle by an amount of correction from
the observer, andthe parameter in the wave-number control is the amount
of correction from the observer.

11. The drive unit of claim 1, whereinthe control section provides the
phase control; and induces only vibration which does not include a
vibration component in a drive direction of a driven object driven by the
vibratory actuator, in the actuator body, by controlling the phase
difference between the plurality of pulse signals, during a predetermined
stand-by period when vibration of the actuator body is started, and
induces vibration which includes the vibration component in the drive
direction, in the actuator body, after the stand-by period has elapsed.

12. The drive unit of claim 1, whereinthe control section provides the
duty-cycle control; and does not move a driven object driven by the
vibratory actuator in a drive direction, by controlling the duty-cycle of
the pulse signal to 50%, during a predetermined stand-by period when
vibration of the actuator body is started, and moves the driven object in
the drive direction by varying the duty-cycle of the pulse signal from
50% after the stand-by period has elapsed.

13. The drive unit of claim 11, whereinthe control section sets the number
of pulses included in the burst period to a minimum value with which the
vibration of the actuator body can be maintained during the stand-by
period.

14. The drive unit of claim 12, whereinthe control section sets the number
of pulses included in the burst period to a minimum value with which the
vibration of the actuator body can be maintained during the stand-by
period.

15. The drive unit of claim 1, whereinin the wave-number control, a
minimum number of pulses included in the burst period or a maximum
duration of an idle period during which no pulse signals are output in
the burst period is set to a value with which the vibration of the
actuator body can be maintained.

16. The drive unit of claim 1, whereinwhen decelerating a driven object
driven by the vibratory actuator, the control section adjusts the number
of pulses included in the burst period to a value less than a minimum
value with which the driven object can be driven.

17. The drive unit of claim 1, whereinin the wave-number control, the
control section adjusts the number of pulses in a normal waveform, each
having a predetermined pulse width, included in the burst period; and
outputs one or more short pulses each having a pulse width shorter than
that of the pulses in the normal waveform during an idle period during
which no pulses in the normal waveform are output in the burst period.

18. The drive unit of claim 17, whereinthe control section outputs the one
or more short pulses only in a latter portion of the idle period.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This application claims priority to Japanese Patent Application No.
2009-053959 filed on Mar. 6, 2009, the disclosure of which including the
specification, the drawings, and the claims is hereby incorporated by
reference in its entirety.

BACKGROUND

[0002]1. Field of Technology

[0003]The present disclosure relates to a drive unit having a vibratory
actuator.

[0004]2. Description of Related Art

[0005]A drive unit having a vibratory actuator is conventionally known.
For example, a vibratory actuator included in a drive unit, disclosed in
Japanese Unexamined Patent Application Publication No. H09-191669, is
formed using a piezoelectric element, and induces vibration in the
piezoelectric element by applying two alternating current (AC) voltages
to the piezoelectric element, thereby allowing a driving force to be
output.

[0006]In this drive unit, frequency control, which varies the frequency of
the two AC voltages, and voltage control, which varies the voltage value
of the two AC voltages, are provided in combination in order to control
the driving force of the vibratory actuator.

SUMMARY

[0007]However, as described above, when a driving force is controlled by
frequency control and/or voltage control, a dead zone is wide in a range
in which a required driving force is small. Specifically, when the
frequency of the two AC voltages is largely shifted from a resonant
frequency of the piezoelectric element, or when the voltage value of the
two AC voltages is excessively reduced in an attempt to reduce vibration
of a piezoelectric element, sufficient vibration is not induced in the
piezoelectric element, thus a low driving force cannot be properly
output.

[0008]Meanwhile, in phase control, which controls a driving force by
changing the phase difference between two AC voltages, the frequency of
the AC voltages is not significantly shifted from a resonant frequency of
the piezoelectric element, and an adequate voltage is ensured as well.
Thus, the dead zone is narrow in a range in which a driving force is
small, and a low driving force can be properly output.

[0009]However, in phase control, even when only a low driving force is
output, the voltage value of the AC voltages is the same as when a high
driving force is output, thereby creating a problem in that power
consumption is high for a low driving force.

[0010]The disclosed technology is directed to overcoming the foregoing and
other disadvantages, and the object of the disclosed technology is to
properly output a low driving force, and to reduce power consumption
associated therewith.

[0011]A drive unit according to this disclosure includes a vibratory
actuator having an actuator body formed using a piezoelectric element,
and configured to output a driving force by vibration of the actuator
body, and a control section configured to induce vibration in the
actuator body by supplying a plurality of pulse signals to the
piezoelectric element; and the control section provides, in combination,
phase control, which controls the driving force by adjusting a phase
difference between the plurality of pulse signals, and wave-number
control, which controls the driving force by adjusting the number of
pulses included in a predetermined burst period in each of the pulse
signals.

[0012]Alternatively, a drive unit according to this disclosure includes a
vibratory actuator having an actuator body formed using a piezoelectric
element, and configured to output a driving force by vibration of the
actuator body, and a control section configured to induce vibration in
the actuator body by supplying a single-phase pulse signal to the
piezoelectric element; and the control section provides, in combination,
duty-cycle control, which controls the driving force by adjusting a duty
cycle of the single-phase pulse signal, and wave-number control, which
controls the driving force by adjusting the number of pulses included in
a predetermined burst period in the pulse signal.

[0013]A lens barrel according to this disclosure includes a lens and the
drive unit configured to drive the lens.

[0014]A camera according to this disclosure includes a lens and the drive
unit configured to drive the lens.

[0015]According to the disclosed technology, even if the required driving
force is small, a desired driving force can be properly output using
phase control or duty-cycle control, and power consumption can be reduced
using wave-number control.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016]FIG. 1 is a block diagram illustrating a configuration of a camera
having a drive unit in accordance with an example embodiment.

[0017]FIG. 2 is a front view illustrating a schematic configuration of a
focusing-lens drive section.

[0018]FIG. 3 is an exploded perspective view of an actuator body of an
ultrasonic actuator.

[0019]FIG. 4 is a schematic top view of an actuator body.

[0020]FIG. 5 is a front view illustrating deformation of an actuator body
caused by a first-order mode of stretching vibration.

[0021]FIG. 6 is a front view illustrating deformation of an actuator body
caused by a second-order mode of bending vibration.

[0022]FIGS. 7A-7D are front views each illustrating deformation of an
actuator body caused by composite vibration.

[0023]FIG. 8 is a waveform chart of drive voltages at a maximum number of
pulses.

[0024]FIG. 9 is a waveform chart of drive voltages when the number of
pulses is reduced by 3 per 5 pulses.

[0025]FIG. 10 is a graph illustrating a relationship between a burst rate
of a drive voltage and power consumption.

[0026]FIG. 11 is a graph illustrating a relationship between a burst rate
of a drive voltage and a driving force.

[0027]FIG. 12 is a waveform chart of drive voltages in a case where the
burst period has been changed.

[0028]FIG. 13 is a waveform chart of drive voltages in a case where short
pulses are output in idle periods.

[0029]FIG. 14 is a waveform chart of drive voltages in a case where short
pulses are output only in latter portions of idle periods.

[0030]FIG. 15 is a flowchart of wave-number control.

[0031]FIG. 16 is a block diagram of a phase control section and a variable
delay circuit.

[0032]FIG. 17 is a waveform chart of drive voltages in starting control.

[0033]FIG. 18 is a block diagram illustrating a configuration of a camera
in accordance with the first variation of the first embodiment.

[0034]FIG. 19 is a block diagram illustrating a configuration of a camera
in accordance with the second variation of the first embodiment.

[0035]FIG. 20 is a flowchart of wave-number control in accordance with the
third variation of the first embodiment.

[0036]FIG. 21 is a map defining a relationship between a monitoring
parameter and the number of pulses in a drive unit in accordance with the
second embodiment.

[0037]FIG. 22 is a map defining a relationship between a monitoring
parameter and the number of pulses in accordance with the first variation
of the second embodiment.

[0038]FIG. 23 is a block diagram of a burst control section and a pulse
generation section.

[0039]FIGS. 24A and 24B are maps defining relationships between a
monitoring parameter and either the number of pulses or the pulse width
in accordance with the second variation of the second embodiment. FIG.
24A is a map for a monitoring parameter and the number of pulses, and
FIG. 24B is a map for a monitoring parameter and the pulse width.

[0040]FIG. 25 is a waveform chart of drive voltages in a case where normal
pulses and variable pulses are used in combination.

[0041]FIG. 26 is a perspective view of a part of a lens mechanism of a
camera in accordance with the third embodiment.

[0042]FIGS. 27A and 27B are schematic diagrams of an ultrasonic actuator.
FIG. 27A is a side view, and FIG. 27B is a cross-sectional view along the
line b-b thereof.

[0043]FIGS. 28A and 28B are graphs each illustrating a characteristic in a
stand-by state. FIG. 28A shows a drive signal, and FIG. 28B shows a
position of the drive shaft.

[0044]FIGS. 29A and 29B are graphs each illustrating a characteristic in a
drive state. FIG. 29A shows a drive signal, and FIG. 29B shows a position
of the drive shaft.

[0045]FIG. 30 is a schematic diagram illustrating a temporal change in the
position of a drive shaft and a friction member of a lens frame in a
drive state.

[0046]FIGS. 31A and 31B are graphs illustrating wave-number control in a
stand-by state. FIG. 31A shows a drive signal, and FIG. 31B shows a
position of the drive shaft.

[0047]FIGS. 32A and 32B are graphs illustrating wave-number control in a
drive state. FIG. 31A shows a drive signal, and FIG. 31B shows a position
of the drive shaft.

[0048]FIGS. 33A and 33B are graphs illustrating wave-number control
outputting short pulses in a stand-by state. FIG. 33A shows a
characteristic of a drive signal, and FIG. 33B shows a characteristic of
a drive shaft position.

[0049]FIGS. 34A and 34B are graphs illustrating wave-number control
outputting short pulses in a drive state. FIG. 34A shows a drive signal,
and FIG. 34B shows a position of the drive shaft.

[0050]FIGS. 35A and 35B are graphs illustrating starting control. FIG. 35A
shows a drive signal, and FIG. 35B shows a position of the drive shaft.

DETAILED DESCRIPTION

[0051]Example embodiments will be described below in detail with reference
to the drawings.

First Embodiment

[0052]A camera system 1 which includes a drive unit in accordance with the
first embodiment will now be described with reference to FIG. 1. FIG. 1
is a block diagram illustrating a configuration of a camera.

[0053]The camera system 1 includes an imaging device 11, an imaging
optical system 12, which forms an object image on the imaging device 11,
a reflection mirror 13 provided on an optical axis between the imaging
device 11 and the imaging optical system 12, a parallax detection section
14, which receives light directed by the reflection mirror 13 and detects
a parallax, and a control section 7, which controls a focusing-lens drive
section 16 (described later) provided in the imaging optical system 12.

[0054]The imaging device 11 is formed of a CCD (Charge Coupled Device) or
a CMOS (Complementary Metal Oxide Semiconductor), and converts an object
image formed on an imaging plane to electric signals by photoelectric
conversion.

[0055]The imaging optical system 12 includes a lens group having at least
one focusing lens 15, and a focusing-lens drive section 16, which drives
the focusing lens 15. A detailed configuration of the focusing-lens drive
section 16 will be described later.

[0056]The reflection mirror 13 is provided on an optical axis between the
imaging device 11 and the imaging optical system 12, and is configured to
be switchable between a reflection state, in which the reflection mirror
13 reflects and directs light incident from the imaging optical system 12
to the parallax detection section 14, and a retraction state, in which
the reflection mirror 13 is withdrawn from the optical axis. That is, the
reflection mirror 13 will be in the reflection state when detecting a
parallax of an object image for an auto-focusing process, and will be in
the retraction state when exposing the imaging device 11 to light.

[0057]The parallax detection section 14 detects a parallax of an object
image. For example, the parallax detection section 14 includes a
condenser lens, a separator lens, and a line sensor. Light incident on
the condenser lens is collected by the condenser lens, and is input to
the separator lens. The light is divided by pupil division in the
separator lens, and is focused onto two points on the line sensor. Thus,
an output signal of the line sensor is output from the parallax detection
section 14.

[0058]The control section 7 controls the focusing-lens drive section 16 of
the imaging optical system 12 based on the output signals from the
imaging device 11 and the parallax detection section 14, and focuses the
object image on the imaging plane of the imaging device 11. A detailed
configuration of the control section 7 will be described later.

[0059][Configuration of Focusing-Lens Drive Section]

[0060]A detailed configuration of the focusing-lens drive section 16 will
now be described with reference to FIG. 2. FIG. 2 illustrates a schematic
configuration of the focusing-lens drive section 16.

[0061]The focusing-lens drive section 16 includes an ultrasonic actuator
2, a lens-holding mechanism 8, and a position detection section 84. The
ultrasonic actuator 2 and the control section 7 form the drive unit.

[0062]The lens-holding mechanism 8 includes a guide pole 81, a movable
case 82, to which the ultrasonic actuator 2 is attached, and which is
configured to be movable with respect to the guide pole 81, and a holding
frame 83, which holds the focusing lens 15 and is integrally attached to
the movable case 82. The lens-holding mechanism 8 is disposed on a lens
group holder (not shown).

[0063]The guide pole 81 is fixedly provided with respected to the lens
group holder so as to be expandable in parallel with the optical axis of
the imaging optical system 12. An abutment member 81a, which is contacted
by driver elements 49 (described later) of the ultrasonic actuator 2, is
fixedly attached on the guide pole 81. Note that although the guide pole
81 is illustrated as being only one in FIG. 2, there may be provided
multiple ones thereof.

[0064]The movable case 82 is configured so as to accommodate the
ultrasonic actuator 2. The movable case 82 is attached so as to be
slidable with respect to the guide pole 81. That is, the movable case 82
moves relative to the lens group holder.

[0065]The holding frame 83 is integrally attached to the movable case 82,
and holds the focusing lens 15 in a position such that an optical axis
thereof is coincident with the optical axis of the imaging optical system
12. The holding frame 83 moves along the guide pole 81 together with the
movable case 82. That is, the focusing lens 15 held by the holding frame
83 moves along the optical axis of the imaging optical system 12,
according to the movement of the movable case 82.

[0066]The position detection section 84 includes a magnetic sensor 84a and
a magnetic scale 84b. The magnetic scale 84b is attached to the movable
case 82. The magnetic sensor 84a is attached to the lens group holder so
as to face the magnetic scale 84b and be spaced apart by a predetermined
distance from the magnetic scale 84b. The magnetic sensor 84a includes an
MR (magnetoresistive) sensor, which detects a signal from the magnetic
scale 84b, etc.

[0067][Configuration of Ultrasonic Actuator]

[0068]A detailed configuration of the ultrasonic actuator 2 will now be
described with reference to FIGS. 2-7.

[0069]FIG. 3 is an exploded perspective view of an actuator body of the
ultrasonic actuator 2. FIG. 4 is a schematic top view of the actuator
body. FIG. 5 is a front view illustrating deformation of the actuator
body caused by a first-order mode of stretching vibration
(expanding/contracting vibration). FIG. 6 is a front view illustrating
deformation of the actuator body caused by a second-order mode of bending
vibration. FIGS. 7A-7D are front views each illustrating deformation of
the actuator body caused by composite vibration.

[0070]As shown in FIG. 2, the ultrasonic actuator 2 includes an actuator
body 4 which produces vibration, driver elements 49 which output driving
forces of the actuator body 4, a case 5 which accommodates the actuator
body 4, rubber supports 61 each of which is provided between the actuator
body 4 and the case 5, and elastically supports the actuator body 4, and
a rubber biasing member 62 which biases the actuator body 4 toward the
abutment member 81a of the guide pole 81. This ultrasonic actuator 2
forms a vibratory actuator.

[0071]The actuator body 4 has a generally rectangular parallelepiped
shape, which has a pair of generally rectangular principal faces facing
each other, a pair of longer side faces facing each other, orthogonal to
the principal faces, and extending in the longitudinal direction of the
principal faces, and a pair of shorter side faces facing each other,
orthogonal to both the principal faces and the longer side faces, and
extending in the lateral direction of the principal faces. The term
"longitudinal direction" is used herein to describe the longitudinal
direction of the principal faces, and the term "lateral direction" is
used herein to describe the lateral direction of the principal faces.

[0072]The actuator body 4 is a piezoelectric element. As shown in FIG. 3,
the actuator body 4 is formed by alternately stacking five piezoelectric
element layers 41 and four internal electrode layers 42, 44, 43, and 44.
Specifically, the internal electrode layers 42, 44, 43 and 44 are formed
by a first power-supply electrode layer 42, a common electrode layer 44,
a second power-supply electrode layer 43, and another common electrode
layer 44, which are arranged alternately in the stacking direction
(thickness direction) each between a corresponding pair of the
piezoelectric element layers 41. The first power-supply electrode layer
42, the second power-supply electrode layer 43, and the common electrode
layers 44 are each printed on one of the principal faces of the
corresponding piezoelectric element layer 41.

[0073]Each of the piezoelectric element layers 41 is an insulator layer
formed of, for example, a ceramic material such as lead zirconate
titanate; and has a generally rectangular parallelepiped shape, which has
a pair of principal faces, a pair of longer side faces, and a pair of
shorter side faces, as does the actuator body 4. Each of the
piezoelectric element layers 41 includes an external electrode 45a formed
in a longitudinal center portion of one of the longer side faces, an
external electrode 46a formed in a lateral center portion of one of the
shorter side faces, and an external electrode 47a formed in a lateral
center portion of the other one of the shorter side faces.

[0074]Each of the common electrode layers 44 has a generally rectangular
shape provided over substantially the entire surface of the corresponding
principal face of the piezoelectric element layers 41. An extraction
electrode 44a is formed in one of the long-side portions of each of the
common electrode layers 44 so as to extend from a longitudinal center
portion thereof to the external electrodes 45a of the piezoelectric
element layers 41.

[0075]As shown in FIG. 4, each of the principal faces of the piezoelectric
element layers 41 has four regions, which are formed by dividing the
principal faces in half both longitudinally and laterally. The four
regions are grouped into two pairs of regions each having a diagonal
relationship. The first power-supply electrode layer 42 includes a first
set of electrodes 42a and 42b respectively formed in regions of one of
the two diagonal pairs of regions, and a conductive electrode 42c, which
couples the first set of electrodes 42a and 42b to conduct electricity
therebetween. Each of the first set of electrodes 42a and 42b is an
electrode of a generally rectangular shape, and overlaps the common
electrode layers 44 in the stacking direction. A first electrode 42a,
which is one of the first set of electrodes 42a and 42b, includes an
extraction electrode 42d extending to the external electrodes 46a of the
piezoelectric element layers 41.

[0076]The second power-supply electrode layer 43 includes a second set of
electrodes 43a and 43b respectively formed in regions of the other one of
the two diagonal pairs of regions on the principal faces of the
piezoelectric element layers 41, and a conductive electrode 43c, which
couples the second set of electrodes 43a and 43b to conduct electricity
therebetween. Each of the second set of electrodes 43a and 43b is an
electrode of a generally rectangular shape, and overlaps the common
electrode layers 44 in the stacking direction. A second electrode 43a,
which is one of the second set of electrodes 43a and 43b, includes an
extraction electrode 43d extending to the external electrodes 47a of the
piezoelectric element layers 41.

[0077]In the actuator body 4, which is formed by alternately stacking the
piezoelectric element layers 41 and the internal electrode layers 42, 44,
43, and 44, the respective external electrodes 45a of the piezoelectric
element layers 41 align in the stacking direction in the longitudinal
center portion of one of the longer side faces, thereby collectively
forming an integrated external electrode 45. That is, the external
electrode 45 is electrically connected to the extraction electrodes 44a
formed in the common electrode layers 44. Similarly, the respective
external electrodes 46a of the piezoelectric element layers 41 align in
the stacking direction in the lateral center portion of one of the
shorter side faces of the actuator body 4, thereby collectively forming
an integrated external electrode 46. That is, the external electrode 46
is electrically connected to the extraction electrode 42d of the first
power-supply electrode layer 42. Furthermore, the respective external
electrodes 47a of the piezoelectric element layers 41 align in the
stacking direction in the lateral center portion of the other one of the
shorter side faces of the actuator body 4, thereby collectively forming
an integrated external electrode 47. That is, the external electrode 47
is electrically connected to the extraction electrode 43d of the second
power-supply electrode layer 43.

[0078]The driver elements 49 are provided in a longitudinally spaced-apart
relationship to each other on the other one of the longer side faces of
the actuator body 4, in which the external electrodes 45a are not
provided. The driver elements 49 are provided in each location
longitudinally inward a distance of 30-35% of the full length of the
longer side faces from each longitudinal end of the corresponding longer
side face. Each of the location corresponds to an antinode of a
second-order mode of bending vibration of the actuator body 4, which will
be described later, and is a location where the vibration has a maximum
amplitude. Each of the driver elements 49 is formed in a combined shape
of a solid cylinder in the base-end side which is attached to the
actuator body 4, and a hemisphere in the forward-end side. The driver
elements 49 are made of hard material such as ceramic.

[0079]The case 5 is made of resin, and has a generally box-like shape
which has a generally rectangular parallelepiped shape corresponding to
the actuator body 4. The case 5 has no sidewall in a plane corresponding
to the longer side face on which the driver elements 49 are provided, of
the actuator body 4. That is, the side face of the case 5 corresponding
to the driver elements 49 is opened.

[0080]The case 5 with such a configuration accommodates the actuator body
4. In this regard, the driver elements 49 protrude from the case 5. The
rubber supports 61 are respectively provided between one shorter side
face of the actuator body 4 and the case 5, and between the other shorter
side face of the actuator body 4 and the case 5. Although both of the
shorter side faces of the actuator body 4 correspond to antinodes of
longitudinal vibration, the rubber supports 61 can support the actuator
body 4 without adversely affecting longitudinal vibration of the actuator
body 4 due to elasticity of the rubber supports 61. In addition, the
rubber biasing member 62 is provided between one of the longer side faces
of the actuator body 4 and the case 5.

[0081]Each of the rubber supports 61 is formed of conductive rubber which
is silicone rubber filled with metal particles, and has a generally
rectangular parallelepiped shape. The rubber supports 61 elastically
support the actuator body 4 while biasing the actuator body 4 in the
longitudinal direction thereof. In addition, the rubber supports 61
conduct electricity from the external electrodes 46 and 47 of the
actuator body 4 to electrodes (not shown) provided on the case 5.

[0082]Similarly to the rubber supports 61, the rubber biasing member 62 is
also formed of conductive rubber which is silicone rubber filled with
metal particles, and has a generally rectangular parallelepiped shape.
The rubber biasing member 62 is provided to bias the actuator body 4 in
the lateral direction (i.e., the lateral direction corresponds to the
direction to bias). In addition, the rubber biasing member 62 conducts
electricity from the external electrode 45 of the actuator body 4 to an
electrode (not shown) provided on the case 5.

[0083]Thus, supplying power to the terminal electrodes (not shown)
provided on the case 5 allows the actuator body 4 to be supplied with
power through the rubber supports 61 and the rubber biasing member 62.

[0084]The ultrasonic actuator 2 with such a configuration is attached to
the movable case 82 so that the driver elements 49 contact the abutment
member 81a of the guide pole 81. In this regard, the ultrasonic actuator
2 is attached to the movable case 82 so that the rubber biasing member 62
is deformed compressively. That is, the actuator body 4 is biased toward
the abutment member 81a, and the driver elements 49 are pressed against
the abutment member 81a.

[0085]The ultrasonic actuator 2 is supplied with power from the control
section 7 under this condition. Specifically, signal lines extending from
the control section 7 are connected to the terminal electrodes of the
case 5. The external electrode 45 of the actuator body 4 is connected to
ground through the rubber biasing member 62. The external electrodes 46
and 47 are supplied with different AC voltages (hereinafter also referred
to as "drive voltages") through the rubber supports 61. In this regard,
introducing a phase shift between the two drive voltages applied to the
external electrodes 46 and 47 causes drive voltages having a phase
difference therebetween to be respectively applied to the first sets of
electrodes 42a and 42b, which form a pair disposed diagonally on the
principal faces of the piezoelectric element layers 41, and the second
sets of electrodes 43a and 43b, which form the other pair, thereby
inducing in the actuator body 4 both stretching vibration in the
longitudinal direction thereof (so-called "longitudinal vibration") and
bending vibration in the lateral direction thereof (so-called "lateral
vibration").

[0086]In order to efficiently vibrate the actuator body 4, it is
preferable that a frequency of a drive voltage applied to the actuator
body 4 be a resonant frequency or an anti-resonant frequency of
stretching vibration or bending vibration of the actuator body 4. The
resonant frequencies or the anti-resonant frequencies of the actuator
body 4 are affected by the material, shape, etc., of the actuator body 4,
as well as by the supporting forces and the supported locations of the
actuator body 4. That is, the shape, etc., of the actuator body 4 is
designed so that the resonant frequency or the anti-resonant frequency of
a desired mode of stretching vibration and the resonant frequency or the
anti-resonant frequency of a desired mode of bending vibration will be
coincident, and a drive voltage having this resonant frequency or
anti-resonant frequency is applied to the actuator body 4. For example,
the shape, etc., of the actuator body 4 is designed so that the resonant
frequency of the first mode of stretching vibration (see FIG. 5) and the
resonant frequency of the second mode of bending vibration (see FIG. 6)
are coincident, a phase shift is introduced between two drive voltages of
a frequency near the resonant frequency, and then, the drive voltages are
respectively applied to the external electrodes 46 and 47 of the actuator
body 4. This induces the first mode of stretching vibration and the
second mode of bending vibration in a coordinated manner in the actuator
body 4, thereby causing a sequential shape change as shown in FIGS.
7A-7D.

[0087]Accordingly, each of the driver elements 49 moves in an orbital path
(specifically, a generally elliptical path) in a plane parallel to the
principal faces of actuator body 4, i.e., a plane including the
longitudinal and lateral directions (a plane parallel to the paper in
FIGS. 7A-7D). In this regard, since the driver elements 49 contact the
abutment member 81a of the guide pole 81, each of the driver elements 49
increases friction force on the abutment member 81a as moving in one
direction along a longitudinal direction of the guide pole 81 during the
orbital movement, and reduces friction force on the abutment member 81a
as moving in the other direction along the longitudinal direction of the
guide pole 81. That is, a driving force is output from the driver
elements 49 to the abutment member 81a when the friction force between
the driver elements 49 and the abutment member 81a increases, thus the
ultrasonic actuator 2 moves relative to the abutment member 81a. In this
embodiment, the ultrasonic actuator 2 moves together with the movable
case 82 along the guide pole 81. The longitudinal direction of the guide
pole 81 corresponds to the drive direction.

[0088]The two driver elements 49 move in orbital paths at a phase shift of
180°. That is, the driving forces are output alternately from the
two driver elements 49, thereby causing the ultrasonic actuator 2 to
move.

[0089]Note that the direction of the driving forces output by the driver
elements 49 can be reversed by switching between conditions whether the
phase of one drive voltage is advanced or delayed with respect to the
phase of the other drive voltage when a phase shift is introduced between
the two drive voltages.

[0090][Configuration of Control Section]

[0091]Next, the control section 7 will be described. The control section 7
includes a target-position setting section 71, a subtracter 72, a
position control section 73, a burst control section 74, a pulse
generation section 75, a phase control section 76, a variable delay
circuit 77, and a first and a second amplifier sections 78a and 78b. In
order to control the focusing-lens drive section 16, the control section
7 provides phase control, which varies the phase difference between the
two drive voltages applied to the ultrasonic actuator 2, and wave-number
control, which varies the wave number (i.e., the number of pulses) of
each voltage wave included in the drive voltages.

[0092]The target-position setting section 71 includes a phase-difference
computation section 71a, which receives the output signal of the parallax
detection section 14, a contrast evaluation section 71b, which receives
the output signal of the imaging device 11, a focus-error computation
section 71c, which receives the output signals of the phase-difference
computation section 71a and the contrast evaluation section 71b, and an
AF-algorithm execution section 71d, which receives the output signal of
the focus-error computation section 71c. The target-position setting
section 71 computes a target position for the focusing lens 15 to focus
an object image on the imaging device 11, using either the output signal
of the parallax detection section 14 or the output signal of the imaging
device 11.

[0093]First, a case where a target position for the focusing lens 15 is
computed based on the output signal of the parallax detection section 14
will be described. In this case, auto-focusing (hereinafter also referred
to as "AF") using the so-called phase-difference detection method is
performed.

[0094]The phase-difference computation section 71a computes a phase
difference based on the output signal from the parallax detection section
14. Specifically, the phase-difference computation section 71a determines
a deviation between two distances, one of which is a reference distance
between two object images which would be formed on the line sensor when
the object images are focused on the imaging device 11, and the other of
which is a distance, obtained from the output signal from the line
sensor, between two object images which are actually formed on the line
sensor.

[0095]The focus-error computation section 71c determines whether the focal
position is before or after the object plane, and determines how much the
focusing lens 15 deviates from the focal position, based on the output
signal of the phase-difference computation section 71a (i.e., the
aforementioned deviation).

[0096]The AF-algorithm execution section 71d computes and outputs the
target position for the focusing lens 15 based on the output signal of
the focus-error computation section 71c.

[0097]Next, a case where the target position for the focusing lens 15 is
computed based on the output signal of the imaging device 11 will be
described. In this case, AF using the so-called contrast detection method
is performed.

[0098]The contrast evaluation section 71b computes a contrast value of an
object image based on the output signal of the imaging device 11.

[0099]The focus-error computation section 71c stores the contrast value
computed in the contrast evaluation section 71b, and outputs an output
signal for moving the focusing lens 15 over a predetermined small
distance to the AF-algorithm execution section 71d. The AF-algorithm
execution section 71d computes and outputs the target position for the
focusing lens 15 based on the output signal of the focus-error
computation section 71c, as described previously.

[0100]In this way, in auto-focusing using the contrast detection method,
the focusing lens 15 is moved over a small distance in a stepwise manner,
then a current contrast value is computed and stored, and lastly the peak
of the contrast value is sought. When the peak of the contrast value is
found, the focus-error computation section 71c outputs to the
AF-algorithm execution section 71d an error between a current position
and the position, where the peak of the contrast value is found, of the
focusing lens 15. The AF-algorithm execution section 71d computes and
outputs the target position for the focusing lens 15 based on the output
signal.

[0101]As described above, the AF-algorithm execution section 71d outputs a
target position for the focusing lens 15 regardless of whether
auto-focusing is performed using the phase-difference detection method or
the contrast detection method.

[0102]The subtracter 72 receives the target position for the focusing lens
15 from the AF-algorithm execution section 71d, and the current position,
which represents the actual position of the focusing lens 15 detected by
the position detection section 84. The subtracter 72 calculates the
deviation between the target and the current positions of the focusing
lens 15, and outputs the deviation to the position control section 73.

[0103]The position control section 73 computes an amount of phase control
to be applied to the drive voltages from the deviation between the target
and the current positions of the focusing lens 15, and outputs an output
signal depending thereto to the phase control section 76. More
specifically, the position control section 73 includes a proportional
operation section 73p, an integral operation section 73i, and a
derivative operation section 73d, and computes the amount of phase
control from the deviation using PID (proportional-integral-derivative)
control. More specifically, the proportional term calculated in the
proportional operation section 73p are added to the integral term
calculated in the integral operation section 73i in a first adder 73a,
and the resultant sum is input to a second adder 73b. The second adder
73b also receives the derivative term calculated in the derivative
operation section 73d; and a PID value which is obtained by an addition
operation of the proportional, integral, and derivative terms is output
from the second adder 73b, and input to the phase control section 76. The
sum from the first adder 73a is also input to the burst control section
74. Note that the burst control section 74 may be configured to receive
only either the proportional term from the proportional operation section
73p or the integral term from the integral operation section 73i, instead
of receiving the sum from the first adder 73a.

[0104]The burst control section 74 determines the number of pulses
included in a predetermined period (hereinafter also referred to as
"burst period") based on the sum of the proportional and integral terms
from the position control section 73, that is, a parameter associated
with the phase difference between the drive voltages. The control
operation of the burst control section 74 will be described later.

[0105]The pulse generation section 75 is configured to output a pulse
signal with a predetermined pulse frequency. Specifically, the pulse
generation section 75 outputs pulses, the number of which depends on the
output signal from the burst control section 74, in each burst period
mentioned above. That is, the pulse generation section 75 groups a pulse
group, including one or more pulses, having a duration corresponding to
the burst period, into a burst signal, and continuously outputs the burst
signal with the burst period. For example, when the burst period
corresponds to five pulses, the pulse generation section 75 may output
all the five pulses, or may output, for example, only two of the five
pulses, depending on the output signal from the burst control section 74.
Note that, although the pulses may be output over the entire period of
the burst period as described above, the signal is conveniently referred
to herein as a "burst signal," including this case. The pulse frequency
(i.e., the period of each pulse included in a burst signal) is set to a
value near the resonant frequency of stretching and bending vibrations of
the actuator body 4 mentioned above. The pulse generation section 75
outputs one of two same signals to the first amplifier section 78a as a
first burst signal, and the other to the variable delay circuit 77 as a
second burst signal.

[0106]The second burst signal input to the variable delay circuit 77 is
phase shifted and then output by the variable delay circuit 77.

[0107]More specifically, the variable delay circuit 77 also receives the
output signal from the phase control section 76. The phase control
section 76 determines the amount of phase shift of the second burst
signal with respect to the first burst signal based on the output signal
from the position control section 73. Then, the phase control section 76
outputs an output signal associated with a phase difference therebetween
to the variable delay circuit 77. The variable delay circuit 77 shifts
the phase of the second burst signal based on the output signal from the
phase control section 76, and provides an output to the second amplifier
section 78b.

[0108]The first and the second amplifier section 78a and 78b respectively
amplify the first and the second burst signals input, and respectively
apply the amplified signals as a first and a second drive voltages to the
ultrasonic actuator 2. The first and the second drive voltages are
respectively applied to the external electrodes 46 and 47 of the actuator
body 4.

[0109]Thus, when the first and the second drive voltages are applied to
the actuator body 4, the actuator body 4 produces composite vibration of
stretching vibration and bending vibration, and moves the driver elements
49 in an orbital path. This orbital movement of the driver elements 49
causes the focusing lens 15 held by the holding frame 83 to move along
the guide pole 81, together with the movable case 82. A position of the
moved focusing lens 15 is detected by the position detection section 84,
and is fed back to the subtracter 72.

[0110]Examples of the first and the second drive voltages thus applied to
the ultrasonic actuator 2 are shown in FIGS. 8 and 9. The graphs of the
first and the second drive voltages shown in FIG. 8 (the phases A and B
in the figure represent the first and the second drive voltages,
respectively) show that pulses are continuously output during the entire
period of the burst period, thereby forming continuous waves as a whole.
The second drive voltage has a phase delay of 270° relative to the
first drive voltage. In this embodiment, when the first and the second
drive voltages have a phase difference of 180°, the actuator body
4 produces only bending vibration, thus the driver elements 49 do not
vibrate along the guide pole 81. Therefore, the phases when the first and
the second drive voltages have a phase difference of 180° are
taken as the reference phases. Then, the driving force of the ultrasonic
actuator 2 is adjusted by adjusting the deviation of the phase difference
between the first and the second drive voltages with respect to the
reference phases. That is, if the reference phases are used, the second
drive voltage shown in FIG. 8 can be considered to have a phase delay of
90° relative to the first drive voltage.

[0111]The graphs of the first and the second drive voltages shown in FIG.
9 show that two pulses are output in each burst period, thereby forming
burst waves each having two pulses output in each burst period as a
whole. More specifically, each burst period of the first and the second
drive voltages has a first portion in which two pulses are output, and
the remaining idle period in which no pulses are output. The second drive
voltage has a phase delay of 45° relative to the first drive
voltage in this example. Note that in this embodiment, a pair of a
positive pulse and a negative pulse are counted as one pulse.

[0112]As described above, the control section 7 adjusts the driving force
using both phase control, which varies the phase difference between the
first and the second drive voltages, and wave-number control, which
varies the number of pulses included in the first and the second drive
voltages based on the deviation between the current and the target
positions of the focusing lens 15. Note that phase control and
wave-number control may be provided based on another motion condition
such as speed, instead of the position of the focusing lens 15.

[0113]Phase control will now be described in detail. In the configuration
of the actuator body 4 according to this embodiment, the driving force is
at the maximum when the phase difference between the first and the second
drive voltages is approximately 90°. That is, a phase difference
of approximately 90° provides the best balance between a component
of orbital movement of the driver elements 49 in the direction to
increase the friction force on the abutment member 81a of the guide pole
81, and a component in the longitudinal direction of the guide pole 81,
thereby causing a high driving force to be output. Meanwhile, as the
phase difference approaches 180°, the component of the orbital
movement of the driver elements 49 in the direction to increase the
friction force on the abutment member 81a increases, but in contrast, the
component in the longitudinal direction of the guide pole 81 decreases,
thereby reducing the amount of movement of each of the driver elements 49
in the longitudinal direction of the guide pole 81, thus the driving
force is reduced. Alternatively, as the phase difference approaches
0°, the component of the orbital movement of the driver elements
49 in the longitudinal direction of the guide pole 81 increases, but in
contrast, the component in the direction to increase the friction force
on the abutment member 81a decreases, thereby reducing the
transmissibility of the orbital movement of the driver elements 49 to the
abutment member 81a, thus the driving force is reduced. Accordingly, the
control section 7 adjusts the driving force by adjusting the phase
difference between the first and the second drive voltages in a range of
90° to 270°, using 180° as a reference value. Note
that the phase difference may be adjusted in a range of -90° to
90°, using 0° as a reference value.

[0114]The phrase "increasing a phase difference" as used herein means
adjusting a phase difference so as to approach the phase difference which
causes a maximum driving force (90° or 270°, in this
embodiment), while the phrase "reducing a phase difference" means
adjusting a phase difference so as to approach the phase difference which
causes a minimum driving force (180° in this embodiment).

[0115]In this phase control, the frequency of a drive voltage remains the
frequency which has been set according to a resonant frequency of the
actuator body 4 over the entire range of control, and the voltage value
of a drive voltage is also maintained at a constant value. As a result,
even when a low driving force is to be output, a desired driving force
can be properly output. However, even when the phase difference is near
0°, and the driving force is small, the voltage value of the drive
voltage is maintained at a constant value, thereby causing high power
consumption for a low driving force.

[0116]Thus, the control section 7 controls a driving force using phase
control and wave-number control in combination. As shown in FIG. 10, a
reduction in the number of pulses included in a drive voltage reduces
power consumption. A burst rate shown in the figure is a value obtained
by dividing the duration summed for all the pulses included in one burst
period by the burst period. Specifically, when it is assumed that the
burst period corresponds to five pulses, and if one burst period includes
five pulses, then the burst rate is 100%; and if one burst period
includes one pulse, then the burst rate is 20%. In other words, the
control section 7 provides phase control over the first and the second
drive voltages, and also reduces power consumption by providing
wave-number control. In particular, when a required driving force is
small, the actuator body 4 can be properly vibrated even if the number of
pulses included in a drive voltage is reduced. However, as shown in FIG.
11, a reduction in the number of pulses included in a burst period causes
the driving force to ultimately reach zero before the number of pulses
reaches zero (i.e., the burst rate reaches zero). This means that using
only wave-number control is not sufficient to properly output a low
driving force. Therefore, in wave-number control, the minimum number of
pulses included in a burst period is set to a minimum value (two, in this
embodiment) with which of pulses the driven components, such as the
movable case 82, the holding frame 83, and the focusing lens 15, can be
driven. In this embodiment, the control section 7 controls the driving
force using phase control utilizing drive signals, which are continuous
waves, when a required driving force is relatively large; and controls
the driving force using phase control along with adjusting the wave
number using wave-number control when a required driving force is
relatively small.

[0117]While, in this embodiment, the minimum number of pulses included in
a burst period is set to two, it is not to be construed as limiting to
this value. That is, the minimum number of pulses can be changed by
adjusting the burst period. For example, as shown in FIG. 12, even if the
minimum number of pulses included in a burst period is set to one, the
driven components can be driven by setting the burst period to a time
period corresponding to three pulses.

[0118]In this regard, the minimum number of pulses included in a burst
period, or the burst period itself, may be changed between a case where
the actuator body 4 is vibrated from a stopped state, and a case where
the actuator body 4 has started to vibrate and the vibration is to be
maintained. Specifically, the amount of power required to maintain the
vibration of the actuator body 4 is lower than the amount of power
required to start the actuator body 4 vibrating. Thus, once the actuator
body 4 starts to vibrate, the minimum number of pulses included in a
burst period can be reduced as compared to when the actuator body 4
starts to vibrate, or the burst period can be set shorter when the number
of pulses included in a burst period is set to one. By doing so, power
consumption can be further reduced.

[0119]In other words, a maximum duration of an idle period in which no
pulses are output in a burst period is set to a time period during which
the vibration of the actuator body 4 can be maintained. That is, it may
be configured such that a next pulse is output after starting the
actuator body 4 vibrating by outputting a predetermined number of pulses
and a predetermined idle period has elapsed, and before the vibration of
the actuator body 4 is completely dampened. If the vibration of the
actuator body 4 is allowed to stop, a relatively high voltage and long
time is required to start the actuator body 4 vibrating again. Therefore,
the actuator body 4 can be continuously vibrated, and hence, the
operation of the ultrasonic actuator 2 can be stabilized by setting the
maximum duration of the idle period as described above.

[0120]In addition, when the movable case 82 is decelerated, the number of
pulses may be less than the minimum number of pulses included in a burst
period when the movable case 82 is driven. By doing so, power consumption
associated therewith can be reduced along with adjusting the deceleration
of the movable case 82, hence of the focusing lens 15.

[0121]While it has been described that the first and the second drive
voltages are set so as not to output pulses during the idle periods, it
is not to be construed as limiting. For example, as shown in FIG. 13,
short pulses each having a shorter pulse width than that of the pulses in
normal waveform (i.e., pulses each having a predetermined pulse width
depending on the pulse period (hereinafter also referred to as "normal
pulses")) may be output with the pulse periods even during the idle
periods. In this way, outputting short pulses instead of outputting no
pulses even in the idle periods allows the actuator body 4 to be supplied
with drive voltages although very low. Consequently, the vibration of the
actuator body 4 can be maintained, and hence, the orbital movement of the
driver elements 49 can be maintained. Thus, even with a configuration in
which short pulses are output in the idle periods, since the short pulses
have reduced pulse widths, power consumption can be reduced as compared
to the case of a continuous wave in which normal pulses are continuously
output. In addition, since the burst period can be set longer as compared
to the case where no short pulses are output in the idle periods, it may
be possible to reduce power consumption depending on the condition.

[0122]Moreover, even in a configuration in which short pulses are output
in the idle periods, there is no need to output short pulses over the
entire idle periods, as shown in FIG. 14. That is, it is sufficient to
output only a required number of short pulses needed to maintain the
orbital movement of the driver elements 49. In this regard, it is
preferable that, as shown in FIG. 14, no short pulses be output in an
early portion of each idle period, but a predetermined number of short
pulses be output only in a latter portion (that is, short pulses start to
be output a predetermined time period (a time period corresponding to the
time period needed to output the predetermined number of short pulses)
before the end of each idle period). That is, since the vibration of the
actuator body 4 is dampened toward the end of each idle period, a drive
voltage can be applied at a time when the vibration of the actuator body
4 has been dampened to some degree by outputting short pulses in a latter
portion of each idle period. Thus, the short pulses allow the vibration
of the actuator body 4 to be maintained more effectively, thereby
allowing power consumption to be further reduced. Note that, even in a
configuration in which short pulses are output in a latter portion of
each idle period, the short pulses do not need to be output if the idle
period is short enough for the vibration of the actuator body 4 to be
effectively maintained.

[0123][Wave-Number Control]

[0124]Next, a specific wave-number control provided by the control section
7 will be described in detail with reference to the flowchart of FIG. 15.
Specifically, this wave-number control is provided by the burst control
section 74.

[0125]First, at step Sa1, the monitoring parameter is read. Specifically,
the sum of the proportional term and the integral term output from the
first adder 73a of the position control section 73 is read as the
monitoring parameter. This sum is a parameter associated with the phase
difference between the first and the second drive signals.

[0126]At step Sa2, it is determined whether the monitoring parameter is
greater than a predetermined first threshold or not. The first threshold
is a value indicative of whether to increase the number of pulses or not.
If the monitoring parameter is greater than the first threshold, the
process proceeds to step Sa5, while if the monitoring parameter is less
than or equal to the first threshold, the process proceeds to step Sa3.
At step Sa3, it is determined whether the monitoring parameter is less
than a predetermined second threshold or not. The second threshold is a
value indicative of whether to decrease the number of pulses or not, and
is less than the first threshold. If the monitoring parameter is less
than the second threshold, the process proceeds to step Sa10, while if
the monitoring parameter is greater than or equal to the second
threshold, the process proceeds to step Sa4. At step Sa4, count values of
an up timer and a down timer are reset (i.e., set to zero), and then the
process returns to step Sa1.

[0127]That is, at steps Sa2 and Sa3, it is determined whether the
monitoring parameter is between the first and the second thresholds or
not, and then, if the monitoring parameter exceeds the first threshold,
the process proceeds to step Sa5, and if the monitoring parameter falls
below the second threshold, the process proceeds to step Sa10. Then,
subsequent control processes are performed accordingly. In addition, if
the monitoring parameter is between the first and the second thresholds,
the count values of the up and the down timers are reset.

[0128]Next, a case where the monitoring parameter is greater than the
first threshold will be described. First, at step Sa5, the count value of
the up timer is incremented, and the down timer is reset. Then, at step
Sa6, the count value of the up timer is read. At step Sa7, it is
determined whether the count value of the up timer is greater than a
predetermined third threshold or not. If the count value is less than or
equal to the third threshold, then the process returns to step Sa1, while
if the count value is greater than the third threshold, the process
proceeds to step Sa8.

[0129]In this regard, if the count value is less than or equal to the
third threshold, and the monitoring parameter remains greater than the
first threshold, the process once returns to Sa1, passes through steps
Sa2, Sa5, and Sa6, and then, proceeds again to step Sa7. This time, since
the process has passed step Sa5, the count value of the up timer has been
incremented by one. Thus, steps Sa1, Sa2, and Sa5-Sa7 are repeated as
long as the monitoring parameter remains greater than the first
threshold, and the process proceeds to step Sa8 when the count value of
the up timer finally becomes greater than the third threshold. In other
words, step Sa7 determines whether the monitoring parameter exceeded the
first threshold only temporarily due to noise, etc., or the monitoring
parameter has been greater than the first threshold during a time period
longer than a predetermined first duration corresponding to the third
threshold. The first duration is set to a time period which can be used
as a criterion to decide that a changed state is not temporary. The third
threshold is set to a value corresponding to the first duration.

[0130]Note that, if the monitoring parameter exceeds the first threshold
only temporarily, the answer in step Sa2 will be No while steps Sa1, Sa2,
and Sa5-Sa7 are repeated (more specifically, when step Sa2 is executed
with the monitoring parameter less than or equal to the first threshold),
and then, the process will proceed to step Sa3. The up timer is reset at
step Sa4 or at step Sa10 after step Sa3.

[0131]At step Sa8, based on a decision that the state in which the
monitoring parameter exceeds the first threshold is not temporary, but
continues for some period of time, the number of drive pulses is
incremented by one. After this, at step Sa9, the count value of the up
timer is reset, and the process returns to step Sa1.

[0132]In this regard, although the down timer is not used when the
monitoring parameter is greater than the first threshold, the down timer
may be reset at step Sa5. By doing so, even if the monitoring parameter
repeatedly exceeds the first threshold and falls below the second
threshold every control cycle (i.e., repeating cycle of the flowchart),
it can be ensured that the down timer will be incremented from zero,
using a procedure described below, when the monitoring parameter becomes
less than the second threshold. That is, duration of time during which
the monitoring parameter remains less than the second threshold next time
can be accurately counted.

[0133]Next, a case where the monitoring parameter is less than the second
threshold will be described. If it is determined that the monitoring
parameter is less than the second threshold at step Sa3, the process
proceeds to step Sa10. At step Sa10, the count value of the down timer is
incremented, and the up timer is reset.

[0134]In this regard, although the up timer is not used when the
monitoring parameter is less than the second threshold, the up timer may
be reset. By doing so, even if the monitoring parameter repeatedly
exceeds the first threshold and falls below the second threshold every
control cycle, it can be ensured that the up timer will be incremented
from zero when the monitoring parameter becomes greater than the first
threshold. That is, duration of time during which the monitoring
parameter remains greater than the first threshold next time can be
accurately counted.

[0135]Next, at step Sa11, the count value of the down timer is read. At
step Sa12, it is determined whether the count value of the down timer is
greater than a predetermined fourth threshold or not. If the count value
is less than or equal to the fourth threshold, then the process returns
to step Sa1, while if the count value is greater than the fourth
threshold, the process proceeds to step Sa13.

[0136]In this regard, if the count value is less than or equal to the
fourth threshold, and the monitoring parameter remains less than the
second threshold, the process once returns to Sa1, passes through steps
Sa2, Sa3, Sa10, and Sa11, and then, proceeds again to step Sa12. This
time, since the process has passed step Sa10, the count value of the down
timer has been incremented by one. Thus, steps Sa1-Sa3 and Sa10-Sa12 are
repeated as long as the monitoring parameter remains less than the second
threshold, and the process proceeds to step Sa13 when the count value of
the down timer finally becomes greater than the fourth threshold. In
other words, step Sa12 determines whether the monitoring parameter fell
below the second threshold only temporarily due to noise, etc., or the
monitoring parameter has fallen below the second threshold during a time
period longer than a predetermined second duration corresponding to the
fourth threshold. The second duration is set to a time period which can
be used as a criterion to decide that a changed state is not temporary.
The fourth threshold is set to a value corresponding to the second
duration.

[0137]The fourth threshold is set to a value greater than the third
threshold. This means that the third threshold is used for cases where
the monitoring parameter increases in value, that is, cases where a high
driving force is required. When a high driving force is required, it is
required to increase the number of pulses with high responsivity, and to
rapidly increase the driving force. Accordingly, the third threshold is
set to a relatively low value. Meanwhile, the fourth threshold is used
for cases where the monitoring parameter decreases in value, that is,
cases where a low driving force is required. When the driving force is
decreased, not as high rapidity is required as when the driving force is
increased. Therefore, the fourth threshold is set to a relatively high
value, thereby ensuring to accurately determine whether the state in
which the monitoring parameter falls below the second threshold is
temporary or not. However, the third and the fourth thresholds may be a
same value.

[0138]Note that, if the monitoring parameter falls below the second
threshold only temporarily, the answer in step Sa3 will be No while steps
Sa1-Sa3 and Sa10-Sa12 are repeated (more specifically, when step Sa3 is
executed with the monitoring parameter greater than or equal to the
second threshold), and then, the process will proceed to step Sa4. The
down timer is reset at step Sa4.

[0139]At step Sa13, based on a decision that the state in which the
monitoring parameter falls below the second threshold is not temporary,
but continues for some period of time, the number of drive pulses is
decremented by one. After this, at step Sa14, the count value of the down
timer is reset, and the process returns to step Sa1.

[0140]As described above, in wave-number control, when the monitoring
parameter has been greater than the first threshold, which is the upper
threshold, during a time period longer than the first duration, the
number of pulses is incremented by one. Incrementation of the number of
pulses causes the driving force to be increased. If the time period
during which the monitoring parameter has been greater than the first
threshold is still longer than the first duration even after the
incrementation of the number of pulses, the number of pulses is further
incremented. In this way, the number of pulses is incremented until the
time period during which the monitoring parameter has been greater than
the first threshold no longer exceeds the first duration, or until the
number of pulses reaches the maximum value (i.e., the drive voltage
becomes a continuous wave). Meanwhile, when the monitoring parameter has
been less than the second threshold, which is the lower threshold, during
a time period longer than the second duration, the number of pulses is
decremented by one. Decrementation of the number of pulses causes the
driving force to be decreased. If the time period during which the
monitoring parameter has been less than the second threshold is still
longer than the second duration even after the decrementation of the
number of pulses, the number of pulses is further decremented. In this
way, the number of pulses is decremented until the time period during
which the monitoring parameter has been less than the second threshold no
longer falls below the second duration, or until the number of pulses
reaches the minimum value (i.e., the minimum number of pulses which can
properly vibrate the actuator body 4).

[0141]Thus, controlling the number of pulses based on a parameter
associated with the phase difference between the first and the second
drive signals allows the required driving force to be estimated, and
power consumption to be reduced.

[0142]In addition, stable control over the number of pulses can be
achieved by using the sum of only the proportional term and the integral
term, instead of a PID value of PID control, as the parameter associated
with the phase difference. Specifically, since the derivative term in a
PID value includes high-frequency components, the number of pulses may
rapidly vary if the number of pulses is controlled based on a PID value
including the derivative term. To the contrary, if the number of pulses
is controlled based on the sum of the proportional term and the integral
term, variation of the number of pulses can be made smooth, and stable
control over the number of pulses can be achieved.

[0143][Starting Control]

[0144]In a drive unit with such a configuration, vibration of the actuator
body 4 may not be stable, and the driving force may not be properly
output immediately after start-up of the actuator body 4. In particular,
if start-up is performed using wave-number control with a reduced number
of pulses, some amount of time is needed for the vibration of the
actuator body 4 to be stabilized. Therefore, the drive unit provides the
starting control as described below. This starting control is performed
in the phase control section 76 of the control section 7. FIG. 16 is a
block diagram of the phase control section 76 and the variable delay
circuit 77. FIG. 17 is a waveform chart of drive voltages output by
starting control.

[0145]The phase control section 76 includes a start timer 76a, a cutoff
switch 76b, and an adder 76c.

[0146]The start timer 76a starts counting at the time when the actuator
body 4 starts up, and outputs an output signal to the cutoff switch 76b a
predetermined time after the start-up.

[0147]The cutoff switch 76b receives a PID value from the position control
section 73, in addition to the output signal from the start timer 76a.
The cutoff switch 76b is configured to switch between ON and OFF states
depending on the output signal from the start timer 76a. More
specifically, the cutoff switch 76b switches to an ON state when an
output signal indicating the elapse of a predetermined time is input from
the start timer 76a, and outputs a PID value to the adder 76c, while the
cutoff switch 76b switches to an OFF state when the output signal is not
input, and blocks the output of the PID value to the adder 76c.

[0148]The adder 76c receives a drive-offset correction amount, in addition
to the PID value. The adder 76c adds the drive-offset correction amount
to the PID value, and computes the amount of delay to delay the second
burst signal. The adder 76c outputs the computation result to the
variable delay circuit 77. The drive-offset correction amount is stored
in a memory, etc., and corresponds to a phase difference between the
first and the second drive signals, which is required to induce only
bending vibration, and not to induce stretching vibration, in the
actuator body 4.

[0150]The second burst signal output from the pulse generation section 75
to the variable delay circuit 77 is input to the multi-stage shifter 77a.
The second burst signal input to the multi-stage shifter 77a is output
from the output tap specified by the output-tap switching section 77b,
thereby is output with a phase shift.

[0151]The tap change section 77c selects an output tap, of the multi-stage
shifter 77a, from which a signal is output based on the input amount of
delay, and outputs the selection result as an output signal to the
output-tap switching section 77b.

[0152]The output-tap switching section 77b switches between output taps of
the multi-stage shifter 77a based on the output signal from the tap
change section 77c, and outputs the second burst signal having a
predetermined amount of phase delay.

[0153]When starting control is performed in the phase control section 76
with such a configuration, the first and the second drive voltages appear
as shown in FIG. 17. That is, after start-up of the actuator body 4, the
phase difference is set to approximately 180° during a
predetermined stand-by period, and after the stand-by period has elapsed,
phase control with a predetermined phase difference is provided.

[0154]More specifically, the cutoff switch 76b of the phase control
section 76 is in an OFF state during a time period from start-up of the
actuator body 4 until the stand-by period has elapsed. During this
period, the adder 76c receives only the drive-offset correction amount,
and outputs an amount of delay based only on the drive-offset correction
amount to the tap change section 77c. Thus, the second burst signal
having an amount of phase delay depending on the drive-offset correction
amount is output from the output-tap switching section 77b. The first and
the second burst signals are respectively amplified in the first and the
second amplifier sections 78a and 78b, and are respectively applied to
the external electrodes 46 and 47 of the actuator body 4 as the first and
the second drive voltages (denoted respectively as "Phase A" and "Phase
B" in the figure) having a phase difference corresponding to the
drive-offset correction amount (this phase difference may be zero
depending on the configuration of the actuator body 4, etc.). Only
bending vibration is induced in the actuator body 4, and the driver
elements 49 reciprocate in a direction to press the abutment member 81a
of the guide pole 81 (i.e., in a direction orthogonal to the guide pole
81). As a result, no driving forces are output, and the movable case 82,
and hence, the focusing lens 15, are not moved.

[0155]Meanwhile, after the stand-by period has elapsed after start-up of
the actuator body 4, the cutoff switch 76b changes to an ON state, and
the adder 76c receives a PID value from the position control section 73.
The adder 76c adds the PID value to the drive-offset correction amount,
and inputs an amount of delay based on the resultant sum to the tap
change section 77c. Thus, the second burst signal having an amount of
phase delay depending on the amount of delay is output from the
output-tap switching section 77b. In this way, a predetermined phase
difference is generated between the first burst signal, which is directly
input from the pulse generation section 75 to the first amplifier section
78a, and the second burst signal, which is input from the pulse
generation section 75 through the variable delay circuit 77 to the second
amplifier section 78b. The first and the second burst signals are
respectively amplified in the first and the second amplifier sections 78a
and 78b, and are respectively applied to the external electrodes 46 and
47 of the actuator body 4 as the first and the second drive voltages
having a predetermined phase difference. Stretching vibration and bending
vibration are induced in the actuator body 4 in a coordinated manner,
thus the driver elements 49 move in orbital paths, thereby allowing a
driving force to be output. As a result, the movable case 82, and hence,
the focusing lens 15, are moved.

[0156]As described above, starting control controls such that no driving
forces are output during a time period from start-up of the actuator body
4 until the stand-by period has elapsed, and the driving force starts to
be output after the stand-by period has elapsed. In this regard, the
stand-by period is set to a time period for the vibration of the actuator
body 4 to be stabilized. By doing so, only bending vibration, which dose
not affect driving of the focusing lens 15, is provided during a time
period from start-up of the actuator body 4 until the vibration of the
actuator body 4 is stabilized. This prevents the focusing lens 15 from
being driven when the orbital movement of the driver elements 49 is
unstable.

[0157]Note that starting control does not necessarily need to be provided
with a reduced number of pulses, but may be provided using first and
second drive voltages of continuous waves. However, by providing starting
control with the number of pulses included in a burst period set to a
minimum value, the vibration amplitude can be gradually increased,
thereby preventing an unpredictable behavior due to an unstable vibration
condition in an early stage after the start of driving.

[0158][Advantage of the First Embodiment]

[0159]As described above, according to the first embodiment, controlling a
driving force using phase control and wave-number control in combination
allows the driving force to be properly output, and power consumption
associated therewith can be reduced even when the required driving force
is small.

[0160]In addition, by adjusting the number of pulses included in a burst
period based on the sum of the proportional term and the integral term
output from the first adder 73a of the position control section 73, which
is a parameter associated with the phase difference used in phase
control, the number of pulses can be adjusted by estimating the required
driving force. That is, the phase difference used in phase control varies
depending on the magnitude of the driving force. Therefore, the driving
force can be estimated from the magnitude of the phase difference, and
the number of pulses can be adjusted depending on the driving force.

[0161]Moreover, usage of the sum of the proportional and integral terms in
the position control section 73, which does not include the derivative
term having high-frequency components, as the parameter associated with
the phase difference, allows for a stable control over the number of
pulses.

[0162]In wave-number control, the number of pulses is increased when the
monitoring parameter is greater than the first threshold, while the
number of pulses is decreased when the monitoring parameter is less than
the second threshold. In this way, the number of pulses is maintained
without change while the monitoring parameter varies between the first
threshold, which is the upper threshold, and the second threshold, which
is the lower threshold. Therefore, stable wave-number control is
achieved.

[0163]In addition, the number of pulses is increased when the monitoring
parameter has been greater than the first threshold during a time period
longer than the first duration, while the number of pulses is decreased
when the monitoring parameter has been less than the second threshold
during a time period longer than the second duration. In this way, the
number of pulses is not changed even when the monitoring parameter
exceeds the first threshold or falls below the second threshold
temporarily. Therefore, more stable wave-number control is achieved.

[0164]Furthermore, only bending vibration is induced in the actuator body
4, thereby providing no driving forces during a time period from start-up
of the actuator body 4 until the stand-by period has elapsed, while both
stretching vibration and bending vibration are induced in the actuator
body 4, thereby providing a driving force, after the stand-by period has
elapsed. This prevents the focusing lens 15 from being driven in a
situation where the orbital movement of the driver elements 49 is
unstable.

[0165][First Variation]

[0166]Next, the first variation of the first embodiment will be described
with reference to FIG. 18. FIG. 18 is a block diagram illustrating a
control section according to the first variation.

[0167]The first variation is different in the configuration of the control
section from the first embodiment described previously. Thus, the same
reference numerals as those of the first embodiment are used to represent
equivalent elements, and the explanation thereof will be omitted.

[0168]Comparing with the first embodiment, a position control section 273
of a control section 207 according to the first variation inputs a PID
value calculated by PID control to both the burst control section 74 and
the phase control section 76.

[0169]Even with this configuration, the burst control section 74 can
control the number of pulses based on a parameter associated with the
phase difference between the first and the second drive voltages.
Accordingly, the driving force can be properly output, and power
consumption associated therewith can be reduced even when the required
driving force is small.

[0170]However, since the PID value includes the derivative term having
high-frequency components, the first embodiment which controls the number
of pulses using the proportional and the integral terms is preferred in
the viewpoint of stable control over the number of pulses.

[0171][Second Variation]

[0172]Next, the second variation of the first embodiment will be described
with reference to FIG. 19. FIG. 19 is a block diagram illustrating a
control section according to the second variation.

[0173]The second variation is different in the configuration of the
control section from the first embodiment described previously. Thus, the
same reference numerals as those of the first embodiment are used to
represent equivalent elements, and the explanation thereof will be
omitted.

[0174]A position control section 373 of a control section 307 according to
the second variation outputs a PID value calculated by PID control
similarly to the first variation.

[0175]Furthermore, the control section 307 includes an observer 379
designed based on models of the focusing lens 15, the lens-holding
mechanism 8, and the ultrasonic actuator 2. The observer 379 receives a
current position of the focusing lens 15 from the position detection
section 84, and the PID value from the position control section 373. The
observer 379 compares an expected operation of the focusing lens 15
according to the model with an operation of the actual focusing lens 15
using both the PID value and the current position of the focusing lens
15, and calculates a correction value to correct the PID value so that
the actual focusing lens 15 will operate in a similar manner to that of
the model. Specifically, a correction value is output so as to reduce the
driving force when the actual focusing lens 15 has moved a distance
greater than that of the model, while a correction value is output so as
to increase the driving force when the actual focusing lens 15 has moved
a distance less than that of the model.

[0176]After this, the PID value from the position control section 373 and
the correction value from the observer 379 are input to an adder 379a,
and the sum thereof (i.e., a corrected PID value) is input to the phase
control section 76.

[0177]In this regard, the burst control section 74 is configured to
receive the correction value from the observer 379. The correction value
from the observer 379 is also a parameter associated with the phase
difference between the first and the second drive voltages, and also
varies smoothly. Therefore, the burst control section 74 can provide
stable control over the number of pulses.

[0178][Third Variation]

[0179]Next, the third variation of the first embodiment will be described
with reference to FIG. 20. FIG. 20 is a flowchart of wave-number control
according to the third variation.

[0180]The third variation is different in the process of wave-number
control from the first embodiment described previously.

[0181]In wave-number control of the third variation, although the number
of pulses is tentatively increased or decreased when the monitoring
parameter has been greater than a predetermined threshold during a time
period longer than a predetermined duration, the number of pulses is
restored to the original value (value before the increase or decrease)
after a predetermined holding time has elapsed. Thereafter, if the
monitoring parameter has again been greater than the threshold during a
time period longer than the predetermined duration, the number of pulses
is ultimately increased or decreased.

[0182]More specifically, at steps Sb1-Sb9 in wave-number control of the
third variation, it is determined whether or not the monitoring parameter
has been greater than a predetermined first threshold during a time
period longer than a predetermined first duration (corresponding to a
third threshold), and if the answer is Yes, then the number of pulses is
incremented by one, and the up timer is reset. Steps Sb1-Sb9 are the same
or similar to steps Sa1-Sa9 of the first embodiment. However, the
increment in the number of pulses is only tentative in this variation,
thus the number of pulses is restored to the original value after a
predetermined holding time has elapsed.

[0183]More specifically, at step Sb10 (after the up timer is reset), it is
determined whether the count value of the holding timer is zero or not.
If the count value of the holding timer is zero, the process proceeds to
step Sb11, while if the count value of the holding timer is not zero, the
process proceeds to step Sb15. At step Sb15, the holding timer is reset
and the process returns to Sb1.

[0184]At step Sb11, the count value of the holding timer is incremented.
At step Sb12, the count value of the holding timer is read, and at step
Sb13, it is determined whether the count value is greater than a fifth
threshold or not. If the count value is less than or equal to the fifth
threshold, the process repeats steps Sb1-Sb13, while if the count value
is greater than the fifth threshold, the process proceeds to step Sb14,
and then, the number of pulses is decremented by one (i.e., restored to
the original value). Thereafter, the process returns to Sb1.

[0185]That is, during steps Sb11-Sb14, the state where the number of drive
pulses has been incremented by one at step Sb8 is maintained for a
predetermined first holding time, corresponding to the fifth threshold;
and after the first holding time has elapsed, the number of pulses is
restored to the original value.

[0186]In this regard, cases where the monitoring parameter increases in
value, that is, cases where a higher driving force is required, include a
case where the movable case 82 driven by the ultrasonic actuator 2 is
obstructed by some foreign object, a case where a foreign object is
caught between the driver elements 49 and the abutment member 81a of the
guide pole 81, a case where a friction force momentarily increases due to
irregular movement or manufacturing error of the driver elements 49 and
the abutment member 81a, etc., many of which are temporary. Therefore,
the number of pulses is increased only for the first holding time to
increase the driving force, and after the first holding time has elapsed,
the number of pulses is restored to the original value. If a higher
driving force is only required temporarily, the required driving force is
decreased after the first holding time has elapsed. As such, even if the
number of pulses is restored to the original value, the monitoring
parameter will be less than or equal to the first threshold. In other
words, the required driving force can be output with the original number
of pulses and the phase difference corresponding to the monitoring
parameter less than or equal to the first threshold. Note that the first
holding time is set to a time period during which the required driving
force is expected to continue to be higher when the required driving
force is temporarily increased, and that the fifth threshold is set to a
value corresponding to the first holding time.

[0187]Meanwhile, a higher driving force may be required not temporary, but
continuously. In such a case, even if the monitoring parameter is once
reduced to less than or equal to the first threshold by increasing the
number of pulses, the monitoring parameter becomes greater than the first
threshold again when the number of pulses is restored to the original
value. Accordingly, after the process returns from step Sb14 to step Sb1,
the process repeats steps Sb1, Sb2, and Sb5-Sb7 described previously, and
proceeds to step Sb8, where the number of pulses is incremented by one.
Thereafter, the process proceeds through step Sb9 to step Sb10. In this
regard, since the holding timer has been incremented in the previous loop
at steps Sb11-Sb13, it is determined that the holding timer is not zero
at step Sb10, and the process proceeds to step Sb15. At step Sb15, the
holding timer is reset, and then, the process returns to step Sb1.

[0188]That is, if a higher driving force is required continuously, the
monitoring parameter becomes greater than the first threshold, and hence,
the process proceeds through steps Sb1, Sb2, and Sb5-Sb7 to step Sb8,
where the number of pulses is incremented by one. However, the process
does not proceed to steps Sb11-Sb14, but returns to step Sb1. Since the
process does not pass through step Sb14 in this case, the number of the
pulses incremented by one is maintained. That is, in a case where the
number of pulses is once tentatively incremented by one, and restored to
the original value, and then, the monitoring parameter has been greater
than the first threshold during a time period longer than the first
duration again, the number of pulses is ultimately incremented by one,
and is not restored to the original value. As a result, an increment of
the number of pulses by one causes the driving force to increase. If this
driving force is greater than the required driving force, the phase
difference is controlled so as to be reduced, thus the monitoring
parameter is reduced. Thereafter, if the monitoring parameter is greater
than the first threshold even after the driving force is increased due to
an incrementation of the number of pulses, the number of pulses is
tentatively incremented, and depending on the condition, is ultimately
incremented as described previously, since the holding timer has been
reset at step Sb15. This tentative or ultimate incrementation of the
number of pulses is repeated until the time period during which the
monitoring parameter has been greater than the first threshold no longer
exceeds the first duration, or until the number of pulses reaches the
maximum value (i.e., the drive voltage becomes a continuous wave).

[0189]Note that the phrase "not restored to the original value" is used
herein to describe that the number of pulses is not purposefully restored
to the original value as is done at step Sb14; and is not intended to
mean that the number of pulses is not decremented any more even after the
monitoring parameter decreases in value. That is, if the monitoring
parameter decreases in value thereafter, it is possible that the number
of pulses is decremented by the process at and after step Sb16, which
will be described later.

[0190]While the cases where the monitoring parameter increases in value
have been described, the number of pulses is also controlled in a similar
way in cases where the monitoring parameter decreases in value.

[0191]More specifically, at steps Sb1-Sb3 and Sb16-Sb20, it is determined
whether or not the monitoring parameter has been less than a
predetermined second threshold during a time period longer than a
predetermined second duration (corresponding to a fourth threshold), and
if the answer is Yes, then the number of pulses is decremented by one,
and the down timer is reset. Steps Sb1-Sb3 and Sb16-Sb20 are the same or
similar to steps Sa1-Sa3 and Sa10-Sa14 of the first embodiment. However,
the decrement in the number of pulses is only tentative in this
variation, thus the number of pulses is restored to the original value
after a predetermined holding time has elapsed.

[0192]Specifically, at step Sb21 (after the down timer is reset), it is
determined whether the count value of the holding timer is zero or not.
If the count value of the holding timer is zero, the process proceeds to
step Sb22, while if the count value of the holding timer is not zero, the
process proceeds to step Sb26. At step Sb26, the holding timer is reset
and the process returns to Sb1.

[0193]At step Sb22, the count value of the holding timer is incremented.
At step Sb23, the count value of the holding timer is read, and at step
Sb24, it is determined whether the count value is greater than a sixth
threshold or not. If the count value is less than or equal to the sixth
threshold, the process repeats steps Sb22-Sb24, while if the count value
is greater than the sixth threshold, the process proceeds to step Sb25,
and then, the number of pulses is incremented by one (i.e., restored to
the original value). Thereafter, the process returns to Sb1.

[0194]That is, during steps Sb22-Sb25, the state where the number of drive
pulses has been decremented by one at step Sb19 is maintained for a
predetermined second holding time, corresponding to the sixth threshold;
and after the second holding time has elapsed, the number of pulses is
restored to the original value.

[0195]In this regard, cases where the monitoring parameter decreases in
value, that is, cases where a lower driving force is required, include a
case where after the movable case 82 driven by the ultrasonic actuator 2
is obstructed by some foreign object, the obstruction is removed, and
hence, the load is suddenly reduced, a case where a friction force
momentarily decreases due to irregular movement or manufacturing error of
the driver elements 49 and the abutment member 81a, etc., many of which
are temporary. Therefore, the number of pulses is decreased only for the
second holding time to reduce the driving force, and after the second
holding time has elapsed, the number of pulses is restored to the
original value. If a lower driving force is only required temporarily,
the required driving force is increased after the second holding time has
elapsed. As such, even if the number of pulses is restored to the
original value, the monitoring parameter will be greater than or equal to
the second threshold. In other words, the required driving force can be
output with the original number of pulses and the phase difference
corresponding to the monitoring parameter greater than or equal to the
second threshold. Note that the second holding time is set to a time
period during which the required driving force is expected to continue to
be lower when the required driving force is temporarily decreased, and
that the sixth threshold is set to a value corresponding to the second
holding time.

[0196]Meanwhile, a lower driving force may be required not temporary, but
continuously. In such a case, even if the monitoring parameter is once
increased to more than or equal to the second threshold by reducing the
number of pulses, the monitoring parameter becomes less than the second
threshold again when the number of pulses is restored to the original
value. Accordingly, after the process returns from step Sb25 to step Sb1,
the process repeats steps Sb1-Sb3 and Sb16-Sb18 described previously, and
proceeds to step Sb19, where the number of pulses is decremented by one.
Thereafter, the process proceeds through step Sb20 to step Sb21. In this
regard, since the holding timer has been incremented in the previous loop
at steps Sb22-Sb24, it is determined that the holding timer is not zero
at step Sb21, and the process proceeds to step Sb26. At step Sb26, the
holding timer is reset, and then, the process returns to step Sb1.

[0197]That is, if a lower driving force is required continuously, the
monitoring parameter becomes less than the second threshold, and hence,
the process proceeds through steps Sb1-Sb3 and Sb16-Sb18 to step Sb19,
where the number of pulses is decremented by one. However, the process
does not proceed to steps Sb22-Sb25, but returns to step Sb1. Since the
process does not pass through step Sb25 in this case, the number of
pulses decremented by one is maintained. That is, in a case where the
number of pulses is once tentatively decremented by one, and restored to
the original value, and then, the monitoring parameter has been less than
the second threshold during a time period longer than the second duration
again, the number of pulses is ultimately decremented by one, and is not
restored to the original value (the phrase "not restored to the original
value" is used herein to describe that the number of pulses is not
purposefully restored to the original value, as described previously). As
a result, a decrement of the number of pulses by one causes the driving
force to decrease. If this driving force is less than the required
driving force, the phase difference is controlled so as to be increased,
thus the monitoring parameter is increased. Thereafter, if the monitoring
parameter is less than the second threshold even after the driving force
is decreased due to a decrementation of the number of pulses, the number
of pulses is tentatively decremented, and depending on the condition, is
ultimately decremented as described previously, since the holding timer
has been reset at step Sb26. This tentative or ultimate decrementation of
the number of pulses is repeated until the time period during which the
monitoring parameter has been less than the second threshold no longer
falls below the second duration, or until the number of pulses reaches
the minimum value.

[0198]As described above, in the third variation, if the number of pulses
needs to be increased or decreased, the number of pulses is first
increased or decreased tentatively, and is restored to the original value
to see if the pulse number needs to be changed, and then, the number of
pulses is ultimately increased or decreased if the number of pulses needs
to be increased or decreased again. This approach prevents a control
result of the number of pulses from oscillating due to temporality of a
need to increase or decrease of the number of pulses.

Second Embodiment

[0199]Next, the second embodiment will be described.

[0200]The second embodiment is different in the method of wave-number
control from the first embodiment. Thus, the same reference numerals as
those of the first embodiment are used to represent equivalent elements,
and the explanation thereof will be omitted.

[0201]In the second embodiment, the burst control section 74 has a map
defining a relationship between the value of the monitoring parameter and
the number of pulses. The burst control section 74 determines the number
of pulses based on the monitoring parameter input and the map, and
outputs an output signal depending on the number of pulses to the pulse
generation section 75.

[0202]More specifically, as shown in FIG. 21, the map has a plurality of
regions each associated with a value of the monitoring parameter, and the
number of pulses is assigned to each region such that the number of
pulses increases as the value of the monitoring parameter increases. For
example, the burst control section 74 sets the number of pulses to "3"
when the monitoring parameter is within the second region II, and sets
the number of pulses to "4" when the monitoring parameter is within the
third region III, and then, outputs an output signal accordingly.

[0203]In this way, a map defining a relationship between the value of the
monitoring parameter and the number of pulses allows the monitoring
parameter and the number of pulses to be quickly switched with the same
timing. In particular, power consumption can be quickly reduced when the
required driving force is small.

[0204]Note that a map does not necessarily need to exist. As in the second
variation described later, any configuration may be applied as long as
the number of pulses is determined based on the value of the monitoring
parameter, one example of which is to divide the value of the monitoring
parameter by a predetermined region division width, and thereby
determining the number of pulses based on the division result.

[0205][First Variation]

[0206]As shown in FIG. 22, different maps may be used for a case where the
monitoring parameter is increasing, and for a case where the monitoring
parameter is decreasing.

[0207]For example, if the monitoring parameter has increased from a value
in the second region II to a value in the third region III, the number of
pulses increases from three to four correspondingly. Thus, an increase in
the number of pulses causes the available driving force to increase by
the amount corresponding to the increase in the number of pulses.
Therefore, if the required driving force remains the same, the required
phase difference decreases, and the monitoring parameter also decreases
accordingly. After this, if the monitoring parameter decreases to the
second region II, then the number of pulses decreases from four to three
correspondingly. Thus, a decrease in the number of pulses causes the
available driving force to decrease by the amount corresponding to the
decrease in the number of pulses. Therefore, even if the required driving
force is the same as before the decrease in the number of pulses, the
required phase difference increases, and the monitoring parameter also
increases accordingly. When the monitoring parameter increases to the
third region III, then the number of pulses increases from three to four
correspondingly as described above. In this way, the number of pulses may
repeatedly increase and decrease across a boundary between regions to
which different numbers of pulses are assigned, which may cause a control
result of the monitoring parameter and the number of pulses to oscillate.

[0208]Thus, the map for a case where the parameter decreases in value
defines each lower limit of the monitoring parameter in the regions to
which the corresponding numbers of pulses are assigned, below each lower
limit in the map for a case where the parameter increases in value. With
this approach, even when the monitoring parameter slightly decreases with
a decrease of the phase difference due to an increase in the number of
pulses, the monitoring parameter does not fall within the next region,
where one smaller number is assigned for the number of pulses, but still
falls within the region where the increased number of pulses is assigned.
This is because the lower limit of each region of the monitoring
parameter is set relatively low in the map for a case where the parameter
decreases in value. In a similar way, even when the monitoring parameter
slightly increases with an increase of the phase difference due to a
decrease in the number of pulses, the monitoring parameter does not fall
within the next region, where one larger number is assigned for the
number of pulses, but still falls within the region where the decreased
number of pulses is assigned. This is because the upper limit of each
region of the monitoring parameter is set relatively high in the map for
a case where the parameter increases in value. Thus, a control result of
the monitoring parameter and the number of pulses can be prevented from
oscillating.

[0209][Second Variation]

[0210]Next, a control unit according to the second variation will be
described with reference to FIG. 23. FIG. 23 is a block diagram of a
burst control section and a pulse generation section.

[0211]Wave-number control according to the second variation determines the
number of pulses based on the value of the monitoring parameter, and also
controls the pulse width of at least one output pulse based on the value
of the monitoring parameter. That is, this wave-number control outputs
normal pulses and at least one pulse (hereinafter also referred to as
"variable pulse") having a pulse width shorter than the pulse width of a
normal pulse in combination.

[0212]A burst control section 474 according to the second variation
includes a number-of-pulse computation section 474a, a number-of-pulse
determination section 474b, and a pulse-width conversion section 474c.

[0213]The number-of-pulse computation section 474a receives the monitoring
parameter and a region division width stored in a memory. The region
division width corresponds to the width of the regions of the monitoring
parameter, to which the corresponding numbers of pulses are assigned in
the map (see FIG. 21). The number-of-pulse computation section 474a
divides the monitoring parameter by the region division width, and
outputs the integer part of the computation result to the number-of-pulse
determination section 474b, and outputs the fraction part thereof to the
pulse-width conversion section 474c.

[0214]The number-of-pulse determination section 474b determines the number
of pulses based on the integer part input from the number-of-pulse
computation section 474a. Specifically, the number-of-pulse determination
section 474b adds "1" to the integer part to obtain the number of pulses.

[0215]The pulse-width conversion section 474c determines the pulse width
of variable pulses based on the fraction part input from the
number-of-pulse computation section 474a. Specifically, the pulse-width
conversion section 474c determines the pulse width in proportion to the
fraction part, with the pulse width of normal pulses taken as "1." For
example, if the value of the fraction part is 0.5, the pulse-width
conversion section 474c sets the pulse width to 1/2 of the pulse width of
normal pulses. Note that the relationship between the value of the
fraction part and the pulse width is not limited to a proportional
relation.

[0216]Thus, the output signal output from the number-of-pulse
determination section 474b and the output signal output from the
pulse-width conversion section 474c are input to a pulse generation
section 475.

[0217]While the above description has been directed to the second
variation in which the number of pulses and the pulse width of variable
pulse are determined, respectively, based on the integer part and on the
fraction part of the value obtained by dividing the monitoring parameter
by the region division width, it is not to be construed as limiting. For
example, as shown in FIGS. 24A and 24B, there may be a map defining the
relationship between the number of pulses and the monitoring parameter
(see FIG. 24A), and a map defining the relationship between the pulse
width and the monitoring parameter (see FIG. 24B); and the number of
pulses and the pulse width of variable pulse may be determined using the
both maps.

[0219]The pulse-signal generation section 475a receives a pulse period,
and generates a continuous wave of pulses output with this pulse period.
The continuous wave of pulses output from the pulse-signal generation
section 475a is input to both the wave-number counter 475b and the burst
gate 475c.

[0220]The wave-number counter 475b receives a burst period, in addition to
the continuous wave of pulses. The wave-number counter 475b counts the
number of pulses included in the continuous wave, and outputs an output
signal for each count of a pulse to both the gate-signal generation
section 475d and the pulse-width-signal generation section 475e. In doing
so, when counting the first pulse of each burst period, the wave-number
counter 475b outputs an output signal different from those output when
the other pulses are counted.

[0221]The gate-signal generation section 475d receives the output signal
from the number-of-pulse determination section 474b, in addition to the
output signal from the wave-number counter 475b; and generates and
outputs an output signal to control the burst gate 475c. The gate-signal
generation section 475d outputs a signal to turn on the burst gate 475c
during a time period from the first pulse of each burst period until the
number of pulses associated with the output signal from the
number-of-pulse determination section 474b are counted.

[0222]The burst gate 475c outputs the continuous wave input from the
pulse-signal generation section 475a only for a time period associated
with the output signal from the gate-signal generation section 475d. This
ensures that as many pulses as a number determined in the number-of-pulse
determination section 474b are output every burst period from the burst
gate 475c.

[0223]The pulse-width-signal generation section 475e receives, in addition
to the output signal from the wave-number counter 475b, the output signal
from the number-of-pulse determination section 474b and the output signal
from the pulse-width conversion section 474c; and generates and outputs
an output signal to control the pulse gate 475f. The pulse-width-signal
generation section 475e determines a timing to output the last pulse of
each burst period using both the output signal from the wave-number
counter 475b and the output signal from the number-of-pulse determination
section 474b; and outputs at that timing a signal to turn on the pulse
gate 475f only for a time period corresponding to the pulse width
associated with the output signal from the pulse-width conversion section
474c.

[0224]The pulse gate 475f receives the output signal from the burst gate
475c in addition to the output signal from the pulse-width-signal
generation section 475e, adjusts the pulse width of the output signal
from burst gate 475c, and provides an output. Specifically, the pulse
gate 475f adjusts the pulse width of a pulse, which passes through at the
timing corresponding to the output signal from the pulse-width-signal
generation section 475e, included in the pulse group input from the burst
gate 475c, to a pulse width corresponding to the output signal. This
allows as many pulses as a number determined in the number-of-pulse
determination section 474b, having the pulse width of the last pulse
adjusted, to be output from the pulse gate 475f every burst period.

[0225]In this way, as shown in FIG. 25, the pulse generation section 475
outputs a burst signal including a combination of one or more normal
pulses and a variable pulse with an adjusted pulse width depending on the
value of the monitoring parameter every burst period. The sum of pulse
widths of the pulses included in a burst signal output as described above
is proportional to the value of the monitoring parameter. Note that the
variable pulse does not necessarily need to be output after the normal
pulses, but may be output before or between the normal pulses.

[0226]As described above, determination the number of pulses and the pulse
width based on the value of the monitoring parameter allows the
monitoring parameter and the number of pulses and the pulse width to be
quickly switched with the same timing. In particular, power consumption
can be quickly reduced when the required driving force is small. In
addition, by changing not only the number of pulses but also the pulse
width based on the value of the monitoring parameter, the driving force
can be continuously adjusted in magnitude. That is, while the number of
pulses is changed only discretely, the pulse width can be changed
continuously, thereby allowing the driving force to be adjusted
continuously in magnitude by adjusting the number of pulses and the pulse
width in combination.

Third Embodiment

[0227]Next, a drive unit according to the third embodiment will be
described with reference to FIGS. 26 and 27A-27B. FIG. 26 is a
perspective view of a part of a lens mechanism 300 of a camera, and FIGS.
27A and 27B are schematic side views of an ultrasonic actuator 302.

[0228]The third embodiment is different in the configuration of the
ultrasonic actuator 302 from the first embodiment. Thus, the same
reference numerals as those of the first embodiment are used to represent
equivalent elements, and the explanation thereof will be omitted.

[0229]The lens mechanism 300 includes a lens frame 310, a lens 311 held by
the lens frame 310, and an ultrasonic actuator 302 attached to an
attachment section 312 of the lens frame 310. The lens frame 310 is
driven by the ultrasonic actuator 302 along the optical axis.

[0230]The ultrasonic actuator 302 includes an actuator body 304, which
generates vibration, an anchor weight 305 attached to one end of the
actuator body 304, and a drive shaft 349 attached to the other end of the
actuator body 304.

[0231]The actuator body 304 is a piezoelectric element, and is formed by
alternately stacking piezoelectric element layers 341 and internal
electrode layers (not shown). The internal electrode layers include a
first group of electrode layers and a second group of electrode layers.
The first group of electrode layers and the second group of electrode
layers are arranged alternately in a stacked manner with the
piezoelectric element layers 341. Specifically, the piezoelectric element
layers 341 are each interposed between a corresponding pair of the first
group and the second group of electrode layers in the thickness
direction. The piezoelectric element layers 341 are each electrically
polarized in the thickness direction, for example, from the first group
to the second group of electrode layers. That is, each two adjacent
piezoelectric element layers 341 are polarized in opposite directions
along the thickness direction. Applying voltage to the first group and
the second group of electrode layers causes each of the piezoelectric
element layers 341 to expand and contract in the thickness direction. In
this regard, although each two adjacent piezoelectric element layers 341
are in opposite relative positions to the first group and the second
group of electrode layers, the directions of polarization are also
opposite. As a result, applying voltage to the first group and the second
group of electrode layers does not cause expanding piezoelectric element
layers 341 and contracting piezoelectric element layers 341 to co-occur
in the actuator body 304, but causes the actuator body 304 to expands all
together and contracts all together as a whole in the stacking direction
(thickness direction) of the piezoelectric element layers 341.

[0232]The anchor weight 305 has a sufficient weight with respect to the
drive shaft 349. The anchor weight 305 is fixedly positioned, and thereby
does not move even when the actuator body 304 produces stretching
vibration. That is, almost all the expansive and contractive displacement
of the actuator body 304 is turned into a displacement of the drive shaft
349.

[0233]The drive shaft 349 is attached to the actuator body 304 such that
the axis thereof is coincident with the stacking direction, i.e.,
expanding and contracting direction, of the actuator body 304. This means
that expansion and contraction of the actuator body 304 causes the drive
shaft 349 to be displaced along the axis thereof according to the
expansive and contractive displacement of the actuator body 304. The
drive shaft 349 holds friction members 313 provided in the attachment
section 312 of the lens frame 310 by friction.

[0234]A pair of the friction members 313 are provided in the attachment
section 312 of the lens frame 310. The friction members 313 are biased so
as to press toward each other by springs 314. A groove 315 having a
V-shaped cross section is formed on a surface facing the mating friction
member 313, of each of the friction members 313. The drive shaft 349 is
sandwiched by the friction members 313 within the grooves 315. In this
configuration, the friction members 313 are biased toward the drive shaft
349 by the springs 314, and friction force is applied between the
friction members 313 and the drive shaft 349. In this way, the lens frame
310 is being held to the drive shaft 349 without moving relative to the
drive shaft 349.

[0235]A control section (not shown) similar to that of the first
embodiment is connected to the ultrasonic actuator 302 having such a
configuration. The ultrasonic actuator 302 is controlled by a drive
voltage from the control section. The drive signal is an AC signal, more
specifically, a pulse signal. In the third embodiment, the control
section provides both duty-cycle control, which varies a duty cycle
(ratio of a pulse width of a positive pulse to a pulse period (the sum of
the pulse widths of a positive (high level) pulse and a negative (low
level) pulse)) of the drive voltages applied to the ultrasonic actuator
302, and wave-number control, which varies the number of pulses included
in the drive voltage. When the actuator body 304 is supplied with a drive
voltage and is actuated, the drive shaft 349 vibrates in the axial
direction thereof. In doing so, an inertial force is applied to the drive
shaft 349 depending on the acceleration of the vibration. If the inertial
force is less than the friction force between the drive shaft 349 and the
friction members 313, the friction members 313, and hence, the lens frame
310 move together with the drive shaft 349. Meanwhile, if the
acceleration increases and the inertial force exceeds the friction force
between the drive shaft 349 and the friction members 313, the drive shaft
349 slides with respect to the friction members 313, thus only the drive
shaft 349 moves.

[0236]A basic configuration of the control section (not shown) of this
embodiment is similar to the control section 7 of the first embodiment.
Specifically, similarly to the first embodiment, the control section
includes a target-position setting section, a subtracter, a position
control section, a burst control section, and a pulse generation section.
In addition to these components, the control section includes a
duty-cycle control section and an amplifier.

[0237]The position control section of this embodiment is different from
the position control section 73 of the first embodiment in that the
position control section of this embodiment computes a duty-cycle control
amount to be applied to the pulse signal based on a deviation between the
target and the current positions of the focusing lens 15, and outputs an
output signal depending thereon to the duty-cycle control section. The
position control section computes the proportional term, the integral
term, and the derivative term from the deviation, and sums up these
terms, thereby computing the duty-cycle control amount. That is, the
position control section computes the duty-cycle control amount using PID
control.

[0238]The burst control section determines the number of pulses included
in each burst period based on the sum of the proportional and the
integral terms from the position control section. This sum of the
proportional and the integral terms is a parameter associated with the
duty cycle of the pulse signal. Thereafter, the burst control section
outputs the output signal associated with the number of pulses to the
pulse generation section.

[0239]The duty-cycle control section determines the duty cycle of the
pulses based on the output signal from the position control section.
Thereafter, the duty-cycle control section outputs an output signal
associated with the duty cycle to the pulse generation section.

[0240]The pulse generation section continuously outputs a burst signal
including, in a burst period, as many pulses as a number depending on the
output signal from the burst control section, each pulse having a duty
cycle depending on the output signal from the duty-cycle control section.
The burst signal output from the pulse generation section is input to the
amplifier.

[0241]The amplifier amplifies the input burst signal, and applies the
amplified signal to the ultrasonic actuator 302 as a pulse signal.

[0242]As described above, the control section of the first embodiment and
the control section of the third embodiment are different in that while a
two-phase drive voltage is output in the first embodiment, a single-phase
drive voltage is output in the third signal, and in that while the phase
difference in the two-phase drive voltage is controlled in the first
embodiment, the duty cycle of the single-phase drive voltage is
controlled in the third embodiment. Also, the part of the variations of
the first embodiment, the second embodiment, and the variations thereof
where control is provided using a parameter associated with the phase
difference can be applied to the third embodiment by providing control
using a parameter associated with the duty cycle. That is, in the third
embodiment, a parameter associated with the duty cycle (e.g., the
proportional term and the integral term of PID control) is used as the
monitoring parameter.

[0243]Next, operation of the ultrasonic actuator 302 will be described in
more detail with reference to FIGS. 28A-28B, 29A-29B, and 30. FIGS. 28A
and 28B are graphs for a stand-by state; FIG. 28A shows the drive signal,
and FIG. 28B shows the position of the drive shaft 349. FIGS. 29A and 29B
are graphs for a drive state; FIG. 29A shows the drive signal, and FIG.
29B shows the position of the drive shaft 349. FIG. 30 illustrates a
temporal change in the position of the drive shaft 349 and one of the
friction members 313 of the lens frame (not shown) in a drive state. In
this embodiment, it is assumed for purposes of illustration that the
actuator body 304 expands when the drive signal is at a high level, while
the actuator body 304 contracts when the drive signal is at a low level.

[0244]When a power supply of the ultrasonic actuator 302 is turned on, a
drive signal in a stand-by state shown in FIG. 28A is applied to the
actuator body 304. The drive signal in a stand-by state has a duty cycle
of 50%. In this case, the actuator body 304 is abruptly displaced upon
both expansion and contraction, thereby causing the drive shaft 349 to
slide with respect to the friction members 313, hence the lens frame 310.
As a result, only the drive shaft 349 is displaced back and forth in the
longitudinal direction, and the lens frame 310 stays in the same
position.

[0245]Meanwhile, in a drive operation, a drive signal shown in FIG. 29A is
applied to the actuator body 304. The drive signal in a drive operation
has a duty cycle different from 50%. For example, the duty cycle is set
to 30% in FIG. 29A. Applied such a drive signal, the actuator body 304 is
abruptly displaced when the drive signal is at a high level (i.e., upon
expansion), while the actuator body 304 is slowly displaced when the
drive signal is at a low level (i.e., upon contraction). As a result, as
shown in FIG. 30, the drive shaft 349 slides with respect to the friction
members 313, thus the lens frame 310 does not move when the actuator body
304 expands, while the friction members 313 are engaged with the drive
shaft 349 by friction force, thus the lens frame 310 is displaced toward
the base end of the drive shaft 349 together with the drive shaft 349
when the actuator body 304 contracts. As such, the lens frame 310 moves
toward the base end, repeating cycles of stop, displacement toward the
base end, stop, displacement toward the base end, . . .

[0246]Note that while the above description has been directed to a case
where sliding with respect to the friction members 313 occurs when the
drive shaft 349 is displaced in one axial direction, and sliding with
respect to the friction members 313 does not occur when the drive shaft
349 is displaced in the other axial direction, it is not to be construed
as limiting. That is, there may be a case where sliding with respect to
the friction members 313 occurs when the drive shaft 349 is displaced in
both one axial direction and the other axial direction. Even in such a
case, the friction members 313, hence the lens frame 310 can be moved.
This is possible because durations of kinetic friction force acting
against the friction members 313 are different for a displacement in one
axial direction and a displacement in the other axial direction of the
drive shaft 349.

[0247]Although a duty cycle of 30% is used in the above example, adjusting
the duty cycle allows the speed of the lens frame 310 to be adjusted. In
addition, while the duty cycle is changed to less than 50% in the above
example, the duty cycle may be changed to greater than 50%. Changing the
duty cycle to greater than 50% allows the lens frame 310 to move toward
the forward end of the drive shaft 349.

[0248]In this way, adjusting the duty cycle of the drive signal allows the
moving direction and the moving speed of the lens frame 310 to be
adjusted. For example, changing the duty cycle toward 50% causes the
moving speed of the lens frame 310 to be reduced, while changing the duty
cycle away from 50% causes the moving speed of the lens frame 310 to be
increased.

[0249]In this duty-cycle control, the frequency of the drive voltage
remains the frequency set depending on a resonant frequency of the
actuator body 304, and also, the voltage value of the drive voltage is
maintained at a constant level across the entire range of control.
Therefore, even when the duty cycle is set near 50% to output a low
driving force, a drive voltage having a frequency depending on a resonant
frequency and having a sufficient voltage value maintained is applied,
thereby allowing a desired driving force to be properly output. However,
despite a low driving force, since the voltage value of the drive voltage
is maintained at a constant value, power consumption is high for a low
driving force.

[0250]Thus, the control section controls a driving force using duty-cycle
control and wave-number control in combination. That is, the control
section reduces power consumption by providing wave-number control over
the drive voltage, while providing duty-cycle control. In particular,
when a required driving force is small, the actuator body 304 can be
properly vibrated even if the number of pulses included in a drive
voltage is reduced. However, a reduction in the number of pulses included
in a burst period causes the driving force to ultimately reach zero
before the number of pulses reaches zero (i.e., the burst rate reaches
zero). Therefore, in wave-number control, the minimum number of pulses
included in a burst period is set to a minimum value (three, in this
embodiment) with which of pulses the driven components, such as the lens
frame 310, can be driven. In this embodiment, the control section
controls the driving force using duty-cycle control utilizing a drive
signal, which is a continuous wave, when a required driving force is
relatively large; and controls the driving force using duty-cycle control
along with adjusting the number of pulses using wave-number control when
a required driving force is relatively small.

[0251]Specifically, the control section applies a pulse signal as shown in
FIG. 31 to the actuator body 304 while in a stand-by state. In a stand-by
state, although there is no need to drive the friction members 313,
resonant vibration needs to be induced in the actuator body 304 in order
to be ready for a rapid transition to a drive state. For the pulse signal
in a stand-by state, the burst period is set to a period of six pulses.
Three pulses are output in the first half of the burst period, and the
rest period corresponding to three pulses is an idle period during which
no pulses are output. During each idle period, a voltage such that the
piezoelectric element layers 341 of the actuator body 304 are displaced
to a neutral position is applied. While pulses are output, the drive
shaft 349 is vibrated depending on the pulses. In the idle periods, the
vibration of the drive shaft 349 is dampened. During this period,
although the magnitude of the vibration of the drive shaft 349 is
reduced, sliding occurs between the drive shaft 349 and the friction
members 313, thereby causing the friction members 313 to stay in
approximately same positions. Even if the friction members 313 are
vibrated together with the drive shaft 349 by friction force, the
vibration of the drive shaft 349 should have been significantly dampened
in such a case, thus the amplitude and the amount of movement thereof
should be small. This idle period is set to a time period during which
the resonant vibration of the actuator body 304 is not completely
dampened.

[0252]Meanwhile, in a drive state, the control section applies a pulse
signal as shown in FIG. 32 to the actuator body 304. The duty cycle is
set to 30% in this pulse signal. In addition, this burst signal outputs
three pulses in the first half of each burst period, and an idle period
corresponding to three pulses is provided in the second half. While
pulses are output, the drive shaft 349 is abruptly displaced when the
pulses are at a high level, while the drive shaft 349 is slowly displaced
when the pulses are at a low level. As a result, the friction members 313
move toward the base end of the drive shaft 349. In the idle periods, the
magnitude of the vibration of the actuator body 304 is gradually reduced,
and vibratory movement becomes symmetrical in terms of the direction
toward the base end and the direction toward the forward end. As a
result, the friction members 313 and the drive shaft 349 slide equally in
both one axial direction and the other axial direction, thereby causing
the friction members 313 to stay in approximately same positions.
However, the resonant vibration of the actuator body 304 is maintained
even in such a case. When a next pulse is output thereafter, the abrupt
and slow vibrations of the actuator body 304 are started again, and the
friction members 313 start to move again.

[0253]Note that, in the idle period, short pulses similar to those of the
first embodiment may be output as shown in FIGS. 33A and 34A. Short
pulses are output both at a high level and at a low level. In addition,
the short pulses are each output at the substantially central time point
in each pulse output period of the normal pulse. Accordingly, in the idle
periods, the period of a short pulse is the same as the pulse period (an
output period for a positive pulse and a negative pulse with a duty cycle
of 50%) both in an idle state and in a drive state. In this way,
outputting short pulses even in the idle periods, instead of outputting
no pulses, allows a drive voltage, although small, to be applied to the
actuator body 304. Thus, the resonant vibration of the actuator body 304
can be maintained. As compared to the case where no short pulses are
output (see FIGS. 31A-31B and 32A-32B), the vibration of the drive shaft
349 is not significantly dampened in the idle periods. In this way, even
with a configuration such that short pulses are output in the idle
periods, since the short pulses have reduced pulse widths, power
consumption can be reduced as compared to the case of a continuous wave
in which normal pulses are continuously output. In addition, since the
burst period can be set longer as compared to the case where no short
pulses are output in the idle periods, it may be possible to reduce power
consumption depending on the condition.

[0254]Moreover, also in this embodiment, starting control similar to that
of the first embodiment is provided as shown in FIGS. 35A and 35B. That
is, the control section outputs a pulse signal having a duty-cycle of 50%
for a time period from start-up of the actuator body 304 until a
predetermined stand-by period has elapsed. Wave-number control is
provided during this time period, and an idle period is provided in the
second half of each burst period. Specifically, during the stand-by
period, the period to output three pulses and the idle period are
repeated, and resonant vibration is induced in the actuator body 304. In
this regard, since the actuator body 304 vibrates equally in both axial
directions of the drive shaft 349, the friction members 313 stay in
approximately same positions. After the stand-by period has elapsed, the
control section outputs a pulse signal having a duty cycle different from
50% to the actuator body 304. This causes the actuator body 304 to
vibrate, moving speed of which is different in one and the other axial
directions of the drive shaft 349, thereby allowing the friction members
313 to move depending on the degree of the asymmetry of the moving speed.
In this regard, wave-number control is provided when a driving force
during start-up is small. In FIG. 35A, idle periods are also provided in
the pulse signal after the stand-by period has elapsed. Note that
starting control does not necessarily need to be provided with the number
of pulses reduced, but may be provided using a pulse signal which is a
continuous wave. In addition, idle periods may only be provided during
the stand-by period (i.e., while a pulse signal having a duty-cycle of
50% is output).

Other Embodiments

[0255]The disclosed technology may be implemented using the configurations
described below in association with the presented embodiments.

[0256]The configuration of the ultrasonic actuator 2 is not limited to the
aforementioned configurations. For example, in the above embodiments, a
configuration has been described in which the driver elements 49 are
provided on a longer side face of the actuator body 4, and the direction
of stretching vibration of the actuator body 4 is aligned with the output
direction of the driving force, while the direction of bending vibration
is aligned with the direction in which the driver elements 49 are pressed
against the abutment member 81a. However, the disclosed technology is not
limited to this particular configuration. Instead, the configuration may
be such that the driver elements 49 are provided on a shorter side face
of the actuator body 4, and the direction of stretching vibration of the
actuator body 4 is aligned with the direction in which the driver
elements 49 are pressed against the abutment member 81a, while the
direction of bending vibration is aligned with the output direction of
the driving force.

[0257]In addition, in the above embodiments, a configuration has been
described in which the driver elements 49 are pressed against the
abutment member 81a, which is a member of the fixed part, while the
ultrasonic actuator 2 is attached to the movable case 82, which is a
member of the movable part, such that the ultrasonic actuator 2 itself is
movable. However, the disclosed technology is not limited to this
particular configuration. That is, the configuration may be such that the
driver elements 49 are pressed against a member of the movable part,
while the ultrasonic actuator 2 is attached to a member of the fixed part
such that the ultrasonic actuator 2 itself is not movable.

[0258]Moreover, while in the above embodiments, the first-order mode of
stretching vibration and the second-order mode of bending vibration are
induced in the actuator body 4, other modes or vibrations may be induced.

[0259]Furthermore, in the above embodiments, the principal faces, each
having a generally rectangular shape in planar view, of the piezoelectric
element layers 41 are each divided into four regions as described
previously, and a different voltage is applied to each diagonally
disposed pair of electrodes. However, the disclosed technology is not
limited to this particular configuration. Four electrodes provided in the
piezoelectric element layers 41 may each be supplied with a different
voltage from the other voltages, or the electrodes may be arranged in a
different way. In such a case, the phase differences between the
plurality of drive voltages applied to the electrodes will be different
from that of the configuration described previously. Specifically, in the
above configuration, the principal faces, each having a generally
rectangular shape in planar view, of the piezoelectric element layers 41
are each divided into four regions as described previously, and a
different voltage is applied to each diagonally disposed pair of
electrodes, thus a phase difference between the two drive voltages of
90° provides a maximum driving force, while a phase difference
between the two drive voltages of 0° or 180° provides a
minimum driving force. However, the phase difference which results in a
maximum or minimum driving force varies depending on the shape of the
piezoelectric element layers 41, the arrangement of the electrodes, etc.

[0260]In addition, while the above embodiments have been described in
which the driving force is controlled using either phase control or
duty-cycle control and wave-number control over one or more drive
voltages in combination, it is in no way intended to exclude frequency
control, voltage-value control, etc., over the drive voltages. That is,
as far as the driving force is controlled using either phase control or
duty-cycle control and wave-number control in combination, frequency
control and/or voltage-value control over the drive voltages may be
additionally provided.

[0261]Moreover, while the above embodiments have been described in which a
member of the movable part (i.e., the movable case 82) is configured to
undergo linear motion, the member of the movable part may be configured
to undergo rotary motion. Specifically, the configuration may be such
that the driver elements 49 are pressed against the periphery of a
disk-shaped body, and the disk-shaped body is rotated as the member of
the movable part; or the ultrasonic actuator 2 is attached to a member of
the movable part, which is rotatable around a predetermined rotation
axis, and the ultrasonic actuator 2 rotates together with the member of
the movable part.

[0262]Furthermore, while the above embodiments have been directed to a
configuration in which the actuator body 4 is formed by a piezoelectric
element, it is not to be construed as limiting. For example, the
configuration may be such that a metallic resonator is formed, a
piezoelectric element is attached to the resonator, and the piezoelectric
element is vibrated, thereby allowing the entire resonator to vibrate. In
this case, the resonator forms the actuator body.

[0263]As described above, the disclosed technology is useful for a drive
unit having a vibratory actuator.

[0264]The present invention is not limited to the presented embodiments,
and may be embodied in other specific forms without departing from its
spirit or essential characteristics. The described embodiments are to be
considered in all respects only as illustrated and not restrictive. The
scope of the invention is, therefore, indicated by the appended claims
rather than by the foregoing description. All changes and modifications
which come within the meaning and range of equivalency of the claims are
to be embraced within their scope.